So, is there gong to be another massive difference between 1.9 and the next version where I'm going to have to relearn everything again?

Dojo is trying to get rid of the design elements present since as early as 2005. In another decade yes, but this whole shift to is geared towards a more stable 2.0. It is the developers who want more change, not the dojo foundation, who is more focused on backward foundation.

And changing the way you access a method (from global variable to requiring them through AMD) is not relearning everything.