But even once it does, I still don’t see an issue. Bitcoin and Grin both have a max mempool size, and you must pay a competitive fee to remain in the mempool in cases where there is high usage. The only way there’s a negligible chance an attacker would have to pay fees is in the case where the fee they chose is too low. When that occurs, their txs would quickly be bumped out of the mempool.
I’m not intentionally trying to be obtuse, but this just seems like such a non-issue, that I really can’t understand why it’s being treated as if it’s some kind of a DoS attack vector. Basic incentives and very minimal and sane mempool policies more than handle these scenarios.