Don't know yet. I only just switched back to CM (from AOSP) now that the theme engine is back. I haven't built a theme for CM12 yet.
I would guess that there shouldn't be any major changes since the theme engine is essentially the same. But, CM is doing some things that don't make much sense to me from a theming perspective. For example, they are using vector drawables instead of PNGs for a lot of things. That makes it easy to change colors, but not to modify the appearance of the icon.This should be relatively easy to fix, but will require extra work. Here's an example where they delete the PNGs and replace with vector drawable xmls: