Remathilis
Legend
This isn't really news. The Dragonborn from Fizban's Treasury of Dragons (from what we've seen in both the UA and the preview of the Metallic Dragonborn) are already split up into 3 separate races, not really being subraces of the same race. And this is fine for most of the races, because most races only have 1-4 subraces. However, it could be a problem for Tieflings and Elves, because they have a ton of subraces. Elves have High Elves, Wood Elves, Dark Elves, Eladrin, Shadar-Kai, Sea Elves, Pallid Elves, and Mark of Shadow Elves, while Tieflings have 9 subraces; one for each layer of the Nine Hells (10 subraces if you include Feral Tieflings). That could get tedious.
I don't imagine all elven subraces will be reprinted in one source. There are only three types of elf in the PHB (high, wood, dark). Eberron had one (shadow mark), ToF had three, Wildemont had one. The extra space used in each book is minimal.
As for tieflings, almost all the tiefling subraces are different ability mods (no longer needed) and innate spells. The only tiefling variant that did anything else was winged. You could just set up a bunch of spell suites and eliminate the need for subraces.