Yes! +1 for @-mentions support! You can already link peoples' names automatically, so we should get notifications / be able to visit a tab on the site that shows everywhere we are mentioned.
I personally wouldn't want chat as a built in feature. Too many features on one front end means lots to learn for everyone. There is a benefit to being all-in-one, but it feels like those people who want to use steemitchat can do that now.
Or at least, people could choose whether they want to be PM'd. And really, if we have mention support, and maybe an additional feature where posts can be private except for the people mentioned…
Anyway, room for lots of basic features first!