As far as I can tell, Vitess still has trouble with cross-server transactions and distributed locking. Presumably something "vastly more scalable" could work around this.

The Spanner team noticeably put out https://cloud.google.com/blog/products/databases/inside-clou... a few years back, which tl;drs that they managed to get a reliable enough network that partitions don't really happen anymore and so you can get both C _and_ A from the CAP theorem. I don't think that Vitess is quite at that level, especially since you can self-host it and thus the devs don't have such network-level uptime guarantees.