It's interesting. First of all, I see OP throwing out the slippery slope argument however I see no reason or evidence that it applies. For example, how would another game that is perhaps 1/10 the population of FFXIV justify a cap to its population "Oh we have suddenly become the most popular game and we don't have enough servers". See how well that will go over with their customers, even if it's a new expansion, typically launches are planned well in advance and congestion is temporary even IF they have one planned during this time of semiconductor backlog.

Secondly, putting a cap on playtime through various means doesn't bother me at all in these exceptional circumstances, likely by capping time through a 24 hour period. I don't care when you play but yes I do think that capping how much you play for the next couple of weeks is going to be fair to everyone. Normally if you want to play for 22 hours out of 24 I would care less, none of my business. Now, after probably around 7 hours (cumulative) you'd get a one hour warning before being logged out.