Frogboy's just dropped the rumored bomb that we will get 'vertical' strategies, ways to win a 4X game without expanding too much. Different games do this different ways... Civ5 had ways to win that worked beat with small empires, and even had a faction that could only really have four cities without conquest (Venice).
Although marketing doesn't want Frogboy's to talk about it yet, we can certainly can. What are your ideas?
I think the key will have to be new ways to win. Especially ways that don't directly compete with expanders. Frogboy suggested allowing more citizens to work a building... Basically making more population on your few planets rather than expanding.
Another possibility is to make expansion more difficult, with fewer people per transport (realistic) and have colonization efforts be a big domestic political issue. Some political situations might favor fewer colonies in exchange for bonuses like the old political party bonuses.
Another way would be to have a cultural victory like in Civ, where all your worlds are paradises. This would then be difficult if you had.more worlds. You could get 'culture points ' based on the population and happiness of a world. More points could give you treats (like alignment), but the treats cost more the more planets you have (each planet has its own culture).
Finally, there could be an economic victory, based on your income per person and/or per planet. The richest population would win. This would emphasize trade as an avenue to victory, but.mighy require more wealth buildings.
The biggest problem I see with all of these ideas is that the vertical empire will naturally be quite vulnerable to larger empires. This deserves some thought.