Most mp games are done as "one turn a day" for most of the early game at least, then extending later. Doing that turn can start out at 10 minutes and run into a couple of hours in late game.
The learning curve? Some will say jump right in after the tutorial. Others will say try out each nation and find the one that matches your style first.
We have gotten insider word that the new project Illwinter is working on is NOT a Dom4.
And a Dom4 is "not in the pipeline"
But we do still get free patches and upgrades once in awhile.
http://ulm.illwinter.com/dom3/dom3progress.html