By all appearances, lots of good stuff in 12.0 and beyond.
I believe we'll be quick out of the gate to deploy it. Much different from 11.x, where my first deployment was on 11.3. Also, they'll be iterating pretty quickly. We expect to see three point releases in calendar 2019, starting with 12.0 in Q1.
In addition to everything
@Cringer mentioned, at long last they're unifying the security models for ABL and SQL. It will be optional and off by default, to provide a compatibility/upgrade path. But you will be able to convert the DB to a model like OE SQL uses today: deny privileges by default, and only allow explicitly. Once a DB is converted, there will be one set of privileges across both query engines. The _file._can-* fields will no longer be used. There will be some refactoring work but it's a great feature and I'm looking forward to it. The work begins in 12.0 and I believe it will be further enhanced, perhaps finished, in 12.1 (currently due mid-year).