There's already working proof of concept for that and have been tested, however it has also some challenges. Currently you can come to chat to talk about issues with logging in into Steem, troubles with Steemit signups, etc. Unfortunately it doesn't support mixed or multi level authorization schemes so the only way is to drop all users that can't for various reasons log in on Steem.
(... and frankly I don't think it's a bad idea... )