I assume you are referring to my point "1", Pablo's current PR for NIP-41?

It's as much required as NIP-26 is required: If your client doesn't support delegated keys it then it won't show them with the correct author, or not show them in the feed at all. In the case of NIP-41 if none of your clients supports it then you loose the connection between the new and the old account (you might not know about the new account).

So for example lets say Pablo needs to renew his key and he uses NIP-41. I decided to keep using an old client that doesn't support NIP-41, I am now going to see his hackers posts. If I'm lucky, someone else we both know will post about his account being hacked and I then decide to follow up and somehow determine what his new npub is (maybe from his github, or because I have another channel with him somewhere). I then manually unfollow his old account and follow his new account. In this sense it is not required. It's a user experience improvement to have NIP-41 support.

The 90 days I wrote was a more or less arbitrary number which I would think is a nice thing to do, a curtesey time that developers give each other in order to give users a better experience.