Despite some users making comments that "this question won't be relevant until decades from now", there is one case where this actually ends up being a problem today.
The same date format you mention, that is used for posts, is used in a lot of different places in the system (e.g. comments, revisions, etc.). One of those places is the expiration date and time for suspensions.
There have been a few cases lately where really long network-wide suspensions have been applied, specifically suspensions with an ending time after 2100. One case where this ended up becoming really confusing is this one, where a user was suspended until 2118, but the timestamp simply showed "
'18", which made users think that it was a bug, that a suspension was supposed to expire but for some reason didn't.
Without a way to represent dates after 2100 in the current global timestamp format, it will create confusing cases like this.
Yes, I'm also aware of this other case of a user suspended until 2292 but the timestamp only showing
'92, but that's much less confusing than the other one.