I imagine 1.6 will, yes, coincide with Mercenaries, both in beta and final release.
Long tangent, somewhat ranting (but really more observation-rambling) commentary:
The delineation between new version, DLC and expansion seems to have gotten a bit muddled over the years. In the early days, before the Internet was ubiquitous, it was vanilla release, then maybe an expansion. Updating the base software when most customers did not have Internet access meant a publisher would have to actually ship out physical media (floppy disks or compact discs) to all of their customers.
I have never worked as a professional software developer and significant insider info, so I can only guess based on bits and pieces, but my conjecture is the 'it will be an expensive hassle to fix anything later' reality made quality a higher priority for releasing software in those days than today, and (again this is sheer conjecture) software was smaller then -- had fewer lines of code -- so there were fewer harbors for bugs to creep in and thus I think (all things being equal, as honest hypothetical conjecturalists must disclaim) it was not as tall of a task to be able to find them all, not requiring as many man-hours.
As time went on, hard drives and RAM got bigger, CPUs got faster, graphics cards got more and more capable of dazzling gamers and computer users with more and more detailed graphics, and to take advantage of the more memory and higher-color and higher-resolution graphics, computer code got longer and longer. Software went from fitting on 80 kilobyte 8-inch floppy disks (before my time) to 5 1/4 inch 360 kilobyte floppy diskettes (originally called minis because they were smaller than the 8 inches) to 720 kilobyte 3 1/2" disks and the higher densities of 1.44 MB to software and games needing more and more disks (I seem to recall several games needing upwards of a dozen 1.44 MB 3 1/2" floppy disks) until we finally got the CD-ROM drive in the 1980s which could hold several hundred MB. But still, too few computers had any internet capacity so updates had to be copied onto physical media and shipped to every customer. The idea of patching software within just a few days or even just a few months after release was practically unheard of, software had to be stable, robust and working as promised on its packaging straight out of the retail box.
There was, technically, DLC in those days -- as early as the Atari 2600 Gameline in the early 1980s -- but it was very rare; most games were pretty much whole as you got them. There were sequels, of course (most of which were actually remakes when you think about them -- Civilization II did not in-game-chronologically follow the original Civilization), and later on "mini-sequels" -- expansions.
It seems like as code has gotten longer and more complicated, so has the taxonomy of code updates -- instead of merely patching bugs, some updates actually added new features. These days, unfortunately, some developers actually block content they actually programmed in at launch and demand users pay extra to unlock that content; this is the gist of "zero-day DLC."
I think Stardock is one of the best when it comes to passing on this tactic. I honestly wish it didn't deserve recognition and respect for this, as I wish it were less rare of a practice ... but unfortunately it does seem rare, so I do give Stardock kudos for it. I'm not sure if anyone else is aware of other devs who continue to support their software through updates many years after launch. Stardock has the more genuine DLC practice in that it actually introduces new stuff, it doesn't feel like the "pay $60 for a trial version, pay $100 or more in total for the real game" tactic several AAA publishers seem to pull. New "tenths" releases (1.1, 1.2, 1.3, etc.) actually add new features without having to pay for DLC. I'm guessing there is some business sense in there, in that continuing development does continue to smolder gamer-to-gamer buzz over features being added and can stimulate new sales on the base game, but what's important from the perspective of being a customer is Stardock's games do tend to get better over time. I think a lot of us who like 4X games such as GalCiv are also fans of Civilization, a"AAA" game that, let's be honest, is a bit more polished -- but updates to Civ from the more prestigious dev die off much more quickly. Sid Meier does not engage his customers as directly, personably and regularly as Brad Wardel does here on Stardock's forums, so its harder to have as much insight into Sid's mindset particularly over time, but the gist of what glimpses I have read here and there from his interviews, speeches and lectures, he does seem to isolate himself more from his customers he considers largely a bunch of whiners, and I think this tends to consider his customers more of cash cows to keep penned in relative to Brad.
This isn't to say I consider Sid evil and Brad a saint; Brad's explicitly stamped me as a 'troll' for attacking his facts and logic on a joeuser political essay/article/whatever-you-want-to-call it a few years back, and there's much I passionately disagree with him on, but aside from the small, niche indie developers (a category inapplicable to Stardock for some time, though they aren't at the AAA level either, I think I've seen Brad note this from time to time) he does seem a lot more respectful of his customers. It was Brad who chiseled the Gamer's Bill of Rights, aborted anti-piracy copyright protections on Stardock Games when he realized despite the popularity of that still-ongoing fad among bigger software publishers that spending money on anti-piracy tech was spending money on something that actually made his products less appealing to customers so there wasn't any real gain to be had, and he continues to drive in longer term support in terms of updating games with brand new free features much longer after release than the AAA guys do.
Stardock has had some flops. I think War of Magic -- the first 'Elemental' title -- is probably the poster child. Unfortunately, it seems, even a very experienced software developer and business manager like Brad can get so caught up in day to day things that they can lose perspective on a cold, hard checklist determination of "Is this read for release?" Stardock gets no points for being perfect on lacking bugs nor even major design flaws. The sad but unfortunate reality is its nearly impossible for that to be the case, I think, given how much code goes into a single release -- no one can really reasonably manage and monitor that much code and other elements (graphics, etc.) in one project. Its kind of like a master gardener having to manage larger and larger gardens that eventually get to be the size of an entire planet. Ginormous amounts of experience can't give you the infinite omniscience to handle an inhuman vastness. What /does/ matter -- again, unfortunate in how rare it is -- is the taking responsibility part. Those of us who forked over cash early, both 'early access' beta buy-inners and those who bought WoM at release -- got every DLC and expansion for free.
Businesses used to do this. Its the right thing to do. And I think it marks Stardock as one of the unfortunately rare companies not treating customers as cash cows to milk dry, and pave over its own mistakes with advertising on new products to bury flops and leaving the paying customers for those flops high and dry. Lots of AAA publishers have released flops and not even considered refunds or credits, they've even lobbied Congress to ensure they will never be required to guarantee any promises they make on the retail boxes -- in the United States, its pretty much caveat emptor (buyer beware) for software and games customers.
I'm not sure how many noticed this, but Galactic Civilizations II recently got an update. THAT WAS NOT A TYPO, I said Galactic Civilizations --II--. TWO. 2! If you missed it, read about it here: https://forums.galciv2.com/473900/page/1/
That seems so crazy, I feel I have to re-iterate this fact a few times. Galactic Civilizations III -- THREE -- 3! -- was released May 14, 2015. SEVEN MONTHS after the official release of this third title in the Galactic Civilizations franchise, Stardock UPDATED THE PREVIOUS VERSION. Can anyone name ANY other publisher who updates a product AFTER its been legacied by a sequel? (do we -really- need to be so desperate to go to George Lucas replacing the Ewoks party for an answer?)