Perhaps existing solutions can be leveraged.
BIP 157 light clients already exclude the spam from their filters by the very nature that they cannot be spent, so the more people who create BIP 157 clients and associated wallet software that removes such unspendable outputs automatically, the less of a problem unlimited OP_RETURN will be.
There are already some light clients out there such as Wasabi and any LN wallet that uses Neutrino, so all we'd have to do is make the SPV method popular again.
Spam will never be filtered from full nodes which means the storage will always be there but network traffic will decrease slightly with this method. SPV should be the default mode of accessing blockchain data.
I still think the best way to do this is to ignore this content. Wallets should continue to ignore this content, whether it's legal or not.
We must keep in mind that OP_RETURN was created to reduce the set of UTXOs, increasing the cost of keeping the node running, removing "garbage" from the blockchain, and reducing the difficulty of detecting spam. OP_RETURN wasn't created to encourage data recording, but to contain the negative effects of something that was already happening. Removing this feature or reducing it further could do more harm than good.
On the other hand, if it increases, it can be harmful because it can generate an increase in illegal content. So, this balanced function must continue to be maintained.
Therefore, what I advocate is that node software continues to ignore this information, so that it can focus on what matters: financial information.
As for the SPV method, I don't think it will be the way to go, because it will further increase the fragility of the decentralization of the network nodes.
