Scalability - Increasing transaction processing capacity and speeds on blockchains to support wider adoption. Issues around block size limits, transition to proof-of-stake, sharding, layer 2 solutions.
Bitcoin community is extremely unlikely agree with PoS and sharding, while increasing block size limit face major resistance. L2 such as LN and side-chain already exist, but very few people use it. So for now, i'd say usage of side-chain and LN should be encouraged by Bitcoin community.
Privacyy - Enhancing privacy protections for users on public blockchains while meeting regulations. Zero knowledge proofs, confidential transactions, mixers/tumblers.
Mixers/tumblers are doing fine for this but I don't know how these and regulations can work together.
Most centralized exchange would take action (e.g. freeze fund or lock account) if you deposit mixed coin though and they'll ask tons of your personal information.