Would it REALLY though?Darkrai should not be tested even with Tera banned as it'd clearly be broken. Nasty Plot, Dark Pulse, Psyshock, and Focus Blast with a Life Orb cleaves through the entire meta at +2 aside from Clefable. It's absolutely still a disgusting mon that has no business being OU. It would literally 'cause Zamazenta usage to increase a lot as the only relevant naturally faster Pokemon that can OHKO Darkrai without using an inaccurate move and shift the meta towards HO since it shits on everything slower.
I think, if anything, Darkrai becomes more broken in a Teraless meta since you can't pop a defensive Tera against it much like Walking Wake becomes really problematic in a Teraless meta, although depending on who you ask, Walking Wake is already a problem in this meta that has Tera.
Not to say that it should for now, as OU already has enough to deal with and would create another Gen 5 Kyu-B situation.
Like honestly OU is dealing with some stuff that are just as or even stronger than Darkrai. Like compared to Sneasler which can sleep you while attacking and is effectively stronger due to its movepool.
After the meta settles, Darkrai should be considered for unbanning (or not if Sneasler ever gets banned like it should uncompetitive piece of shit).