Everything from the original roadmap has shipped:

Former known limitations, both since fixed: concurrent view_submission ACKs no longer serialize in the Socket Mode transport (handlers run off-process and ACK on completion), and message_changed/message_deleted subtypes are fully normalised (text/1, user/1, ts/1, thread_ts/1 and from_bot?/1 read the nested message).

Nothing is currently planned. Ideas welcome — open an issue.