My Reddit habit has been all but replaced with private Slacks and Discords these days. Either hobby / interest groups, or an "alumni Slack" full of old work friends from a company I worked at a long time.
I think that's the future, for geeks and nerds anyway. Small private forums, where you can actually have real discussions without getting drowned in memes and downvotes.
For the masses, I think the cement is pretty much dry at this point. You might see a TikTok replace an Instagram once per decade, or something like that. But whatever people migrate to will probably be extremely similar to the thing they migrated from. It's just what the casual masses want.
I find these terrible for any kind of information discovery. I hate that so many communities are using them as an alternative to a subreddit or focused forum. Hell most "modern" forum software is horrific as well.
I think that the advantage in using some kind of instant-message system like Discord/Slack is that you might end up getting a faster response, which is quite helpful when I'm feeling impatient and want my problem to be solved faster. On the other hand, the questions aren't as easily searchable and archived for future people to find.
I rather like my reaction GIFs and discussion threads. What I want to see is a modern IRC with these features, and an optional per-channel/per-server message persistence to deal with not knowing what happened while you were away, or while the mobile IRC app of your choice was killed by the Google/Apple background task manager that only allows you to dodge it with proprietary push support.
Slack also smacks of terrible usability, and is proprietary up the wazoo. There is no way to automate anything on it unless your organisation gives some approval.
I think that's the future, for geeks and nerds anyway. Small private forums, where you can actually have real discussions without getting drowned in memes and downvotes.
For the masses, I think the cement is pretty much dry at this point. You might see a TikTok replace an Instagram once per decade, or something like that. But whatever people migrate to will probably be extremely similar to the thing they migrated from. It's just what the casual masses want.