Cemu already uses multiple cores. One core is always utilized 100% while the others vary. For Wii U emulation, single-core performance is more important than having many cores.
Compatibility doesn't really classify as a 'new feature' and it wouldn't really make for a good surprise either. In fact, I can say right away that the next release won't have any compatibility improvements. (And no performance improvements either)
No, Decaf doesn't have
H264 support yet.
In regards to Cemu I can say adding H264 playback is an extraordinary amount of work compared to most other important core features, so don't expect it any time soon.