Additionally when it comes to doing work we have no way of distinguishing what hardware was used to perform that work. In other words someone could build a new ASIC to mine the new "slow CPU mining option" and we would be right back where we started.
Despite this not being foolproof, it would be interesting to submit a BIP for adding metadata such as the device used within the GetBlockTemplate RPC, obviously with small size limits.
That would be similar to looking at the output address of the block reward to try to figure out how many miners are mining. It would be trivial for a miner to change the metadata for every block they find.
I don't think any "ASIC resistant" algorithm would be desirable to implement. All it would do would be to make it more difficult to develop ASICs, and there is always the risk that the person advocating for a particular algorithm has already done some research on how to create ASICs for that algorithm.