Species, Backgrounds, and Feats, too.
All of the Species and variant/sub-Species need retooling to remove Ability Score modifiers and some need to be rebalanced with an equivalently useful non-ribbon feature to make up for said loss. Some of the Variant/Sub Species need to be completely reworked due to new assumptions of the base species they modify.
The Siberys Aasimar variants, for example, don't work with MP:MotM and 2024 PHB Aasimar (as they are subspecies that essentially replace the VGtM subspecies, while MP:MotM onward introduced the idea that all Aasimar can access all of these forms, rather than them having forked-at-char-creation lineages a la Elves and Tieflings.
Ruinbound Dwarves similarly don't work with the 2024-revised PHB Dwarf species, as Dwarven lineages were eliminated (in part because while most fantasy species follow the "our x is different" trope model, Dwarves are almost always troped as "our dwarves are all the same" – even when dividing cultures. The way around this would be to create a whole-separate species block for Runibound Dwarves, a la Duergar in MP:MotM.
Dhakaani could be turned into a single species with 3 different lineages/heritages, as opposed to using the terms Goblin/Hobgoblin/Bugbear.
The four backgrounds included all assume 2014-weighted background features, rather than the 2022-Dragonlance-onward "background comes with an origin feat" assumption, and the 2024-PHB-onward "background supplies the Ability Score Bumps" assumption.
Species-feats likely need retooling – as XGtE's species feats and the related DDB/DMGuild "Options for Everyone" species feats may also need signifcant retooling to align with 2024 feat assumptions. If we see significant revisions here beyond a "min. 4th-level" requirement for the feat, it could also speak to what we may expect from an updated "Big Book of Character Options" release that may be forthcoming.