1. MimbleWimble is actively developed, but not for Bitcoin. It lacks support from Bitcoin community, mainly because it's not popular and not compatible with bitcoin script
2. TumbleBit already available today on
Breeze Wallet3. Schnorr Signatures is actively developed, but it took long time since there's no standard for it
4. Confidential Transactions won't coming to Bitcoin since it has scalability trade-off (bigger transaction size and longer verification time). Most privacy-based cryptocurrency use it though
Also, there are few upcoming proposal which are interesting
- Dandelion
- MAST
- Eltoo
- Bulletproof (useless unless CT is used as well)
Edit : looks like Pmalek already answer your question while i verify my memory