> until the spam gets mined of course
Aha! This is the critical point. I don't think we can prevent miners from seeing the spam, but maybe we can discourage mining of those transactions.
People who are against large OP_RETURNs should focus on how to punish the miners that include those transactions. One option is to delay propagation ot those blocks. Delay, not reject, as we don't want to split chains
What do you think? And apologies if you've seen this idea already!