I think many are making presumptions that may not be true about Entrenchment. I've looked at all the pictures and watched the video gameplay, and I'm fairly sure Starbases will be buildable from the game start. There seems to be a Starbase cap, just like Capship cap, so if you want to spend the bucks, I think you will be able to build a base from the get-go.
BUT, I'm sure it will be the most basic of bases, and from what I read, you may have to research and/or buy the expensive upgrades. More importantly, there is a starbase counter: Missle ships.
So the game should not slow down, since if someone seems to be playing like a mega-turtle, you just fast tech to Missle Ships and Super Weapons. Let him turtle; put the Superweapons on autofire, tell your factories to crank out a dozen Missle ships, and go get a snack. Come back and mop up. I don't think it will be longer (unless you play 1v1, both mega turtles, and neither wants to tech to super weapons), just have more units, which have more counters, and the ability to be a defensive player now, not just land-grabbing and rushing.
And I agree with above, I like Sins BECAUSE it's not over in 20 minutes. I play Civ4, online sometimes, those games can go on for weeks, so Sins is almost "speedy" to us. But a time limit, like "Best score in 2 hours" would be very welcome here.