I think one thing could be done in post text-area, that hashtags and mentions should be suggested if user types '#' or '@' and then starts typing. Although I know this would be already in the list. Right 8)
@fastidious20 notes102 replies5 tags, 3 users following4 followersBetter don’t ask, just fastidious.enter to followenter to reply
Not without JS, that I know of.