With hindsight I think what we could/should have done is partition core CSS that would have servered both Base and Bootstrapbase themes from the same stylesheet. A kind of "Do it Once do it for All" scenario.
In fact this could still be achieved by making Base a child theme of Bootstrapbase and losing all core CSS from Base theme but leave page_layout.css.
Call me crazy...but it works!
Cheers
Mary
Not, in MDL-51580 they are discussing completely removing theme_base from Moodle 3.1, not just deprecating it for a few releases.
Moodle should have dropped off Base theme in 3.0
If any one needs it the can download from plugins database.
As I have said in MDL-51580 we hardly get any questions about the older themes in the Themes forum.
We made the transition from 1.9 to 2.0 without too much agrivation. In fact it was good fun...I learnt lots about themes then. Now it's getting more technical...and a little boring.
I don't have any qualms about losing Base at all.
Cheers
Mary