I am having a discussion about downsides in this thread: https://x.com/SuperTestnet/status/1917338559217823862

Some of the anti-filter people say that enhanced filters would harm the mempool because the current crop of spammers would start bypassing the mempool and submitting their transactions to miners directly, which makes the mempool inaccurate a less accurate indicator of what transactions are actually waiting to get mined. That can have downstream effects on fee estimation.