If I'm Brad and Co, I'm devoting the vast majority of "GalCiv" worktime to Galactic Civilization IV. Keep up patches for errors and bugs (that is, errors and bugs that Stardock thinks are errors and bugs, see numerous examples of this: bugs that were reported wayback 2016-2017 and have not been fixed, sometimes one person's Bug is another person's WAI/not worth bothering with issue) for GalCiv3 but certainly no more expansions or DLCs.
I recall frogboy posting about what he felt was the frustation of working hard on free patches and that hard work not being appreciated by some members of GalCivIII World. I imagine they're coming to the point where there's going to be a value/benefit trade-off between putting time into work for GalCivIII or leave it - as unfinished/unpolished as most people seem to think it is (I think diplomacy and espionage are still not where they could be, personally) - where it is and start a Founder's campaign to buy in to the development of GalCivIV.
The one big mistake they made - although I really like Citizens as an idea, however imperfect it's implementation - was making massive, serious changes to how the economy worked partway through GalCivIII's life. Stardock need to - once they've decided how certain core areas of GalCivIV are going to work (Economy, Research, etc) - never change those areas. Refine and improve, yes. Once you start on Road 1, by all means expand it with another lane or add some concrete to make it smoother/faster, but don't suddenly dig it up and build Road 2.