I read that Snyder is confirmed to have shown his cut of the movie to a group of executives at Warner back in January. ( https://www.ign.com/articles/snyder-cut-history-lost-justice-league-movie-real-exist ) So it seems that something is going on. I've long wondered if this would be the next "Superman 2: Richard Donner Cut", but never thought it could happen so quickly.
My active imagination tells me that this Quarantine has been the PERFECT time for Warner to invest in this kind of project, since it requires no additional filming, just a bunch of post-production that can largely be done while in quarantine. (The score might be the one thing that would require quarantine to end, but I've heard of film makers getting creative with that, too.) So if it got the green light back in January (or perhaps in early quarantine, as it may have been more appealing a project at that point) I think it makes sense that it could be ready to go sometime in 2020 (though I have doubts about this summer, unless a lot of visual effects work was already done, which would surprise me).
I would be surprised if it was stranded on HBO Max, at least forever. That strikes me as something you do as a timed exclusive to get people subscribed. They will eventually want it to make money for them wherever it can.
Again, this is all nerdy speculation and wishful thinking. And also assumes that the cut is GOOD! I believe it must be better than what we got, but two previewers at Warner reportedly both used the word "unwatchable" to describe how bad they thought it was. (Despite others highly praising it. This suggests it may be divisive as BvS was, which I LOVED, so I say bring on that division!)
Bottom line: We won't know until we know!