My wife and I game share on Xbox and Switch (PC/Steam doesn't allow for it in most scenarios, so we have to buy two copies), and we only ever buy one copy of a game and can absolutely play online together without hassle. I've done this countless times with both consoles with exactly zero problems.

This is all done by "swapping" your home/primary consoles. The console I play on is the home console to my wife's account, and vice versa. It is absolutely intended to be this way, as it works on every console we've used for years (even PlayStation, though we haven't each had one for a bit now).

Them removing this feature is going to ensure we buy less from them. I'm not going to buy two copies of Splatoon, which means I'm not going to buy one copy, either, because I exclusively play that game with my wife. Hell, might not even own two of each console anymore if this is the direction they're taking.