> - The cost associated with purchasing tokens needed to initialize an account on the blockchain would serve as a spam prevention mechanism; an alternative to SIM cards which most centralized services rely on today as a cost barrier to limit the creation of spam accounts.

Doesn't seem like that to me. If I get banned I can just move my cash to another account and start again, and assuming multiple services does this I can amortize the cost over all of them.

The rest seems to me like something mTLS could solve better.