I could potentially make a separate API that will return URL instantly, and will redirect to Tenor while upload is prepared, and then serve local copy. If you are interested, let me know.
Discussion
There have been a couple comments in my feed from people expecting to paste a nostr.build address so that could be cool
Your API is fast already, it's mostly that nip98 AUTH requires me to publish a Kind 27235 note, which takes time to broadcast with my current library
Were you thinking this API would be separate from nip98?
Nip98 does not require anything, just a signed header. You are talking about nip94, that can be pushed async.
I would probably need that for user uploaded gifs actually now that I think about it more