PeakD already has Cross-Posting which is basically the Resteem+Comment. The user facing side of that is that is works just as you'd expect, but behind the scenes it creates a new post under YOUR account that has the content from that post inside. This clashes a bit with autovoting because since the post is coming from your account it will trigger your autovotes and the beneficiary split on that will go 90% to the original poster with you getting 5%.

Direct Messaging won't work on the blockchain for numerous reasons, but one easy to grasp one is privacy. Steem/Hive are public blockchains so all posts to the chain are public. You typically want DM's to be private.
OpenSeed is working on providing direct messages that apps will be able to integrate onto frontends by having another off-chain database on top of the on-chain information. This would make a lot more features possible, but messaging is the first one we're working on.

I could write a book on all the features I still think are necessary, but I guess the focus now should be getting back to where we were on Steem, then we can hopefully figure out the best path forward and how to thrive.