I do agree on the neat alternative piece, but all of the ones that have come up in the past had some sort of flaw (or in some cases deliberate slower growth) that caused them not to go viral (Voat, Tildes, etc)
I'm honestly flabbergasted that with all the nearly-free money flowing around, nobody tried to build a better Reddit without making it both worse and even MORE filled with spam and nazis.
I suspect in general the entire "thing" that is Reddit is on its way out - just like how craigslist killed classified ads and itself may be slowly dying, Reddit killed forums and now is slowly dying, there may be no replacement.
Good point - the "open source/non-profit" energies seem to be focused on things like mastodon and simple forums, and competitors that aren't trying for venture capital such as Facebook would just want you to use their offering instead. I suspect for many people, "Facebook Groups" is their Reddit replacement.