From user standpoint?
Significant.
No any "modern" approach, let it be - reddit, twitter, hackernews, fb groups, discord, mailing lists maybe? gets even close when it comes to quality/merit of discussions that forum can enable
I agree that from a user perspective it can create very different "illusions" and (over the long run) even modify people's behavior - which is scary if you think about it: simple choices at the technical level can change society
added notifications on reply
removed three-like structure
and allowed threads to be bumped
then you'd have forum which would mean that you'd have longer and deeper discussions
I'm very leery of unmoderated comments these days, but combining focus of a blog with reach of microblogging seems a reasonably decent match.