The interface on old Lemmy is perfect. If a post hot into the front page allowing for seamless connection from your reddit account to Lemmy this site would instantly get millions of new users and probably overtake reddit cause the fedverse is superior.
There’s something a little like this in the form of https://portal.alien.top/
However, as I understand it that currently only works with that specific site/instance (alien.top). Not aware of any others that may do so.