Well, don't expect an official answer to that now. One step at a time, what happens after 1.9 depends on what occurs during its development. Actually, IF Europe does include colonialism (that's still a big if), it might even occur that I'm done with adding rebalancing new game features and might consider only graphical or interface changes.
Also, 1.9 doesn't need to be followed by 2.0. I'd like to keep that number for something that deserves it, like a really finalized, polished release. If 1.9 successor just adds some new things like those before it, it'll be called 1.10.