I am not so sure in it, I think that in this case, all Nostr clients should accept this. Something like hashcash. Otherwise Amethyst can lose a lot of users, since it would load your phone.

And it would be still possible to spam, since spammers can use other clients.

Btw, thanks for Amethyst. I complained a lot about it in past. As for now, I like it even more than Damus. 💜⚡💜