Is there no NIP for relays that implements PoW?

Lets say the user has to :

sha256(1'000'000 x pubkey of user + user chosen random 64bit number)

if the resulting hash has at least the first 7 bits as 0's the message is accepted by relays.

1 million times the pubkey of the user limits it to max gpu acceleration, as most cheap fpga's do not have enough space for it.