None, as it turned out - much to my happiness.

The new version only contains some minor bugfixes.
Because DD-SMEP does not have any AI files it is very tolerant of other mods and new Paradox versions. That's by design.
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There's no need for you or anyone to live without new DD-SMEP versions, all you have to do is take up development yourself. I encourage everyone to apply for my position of developer. Seriously!
For me personally the problem is I don't like to play Vanilla anymore. I like the Doomsday Compendium mod much better - both its philosophy of combining the best parts of different mods into one, and the actual implementation. But Doomsday Compendium isn't compattible with DD-SMEP, it actually has many more excellent events.
I got into modding not for credit, but only to improve my own gaming experience. So I have no reason to develop a mod for a version I stopped playing.