This is what I have learned:

1)Using pubkeys for this reason is inefficient and expensive, which is good. Don’t make it easy to put spam into the blockchain.

2) It’s not a burden if the amount of this transactions is very low. Which from my understanding is the case.

3) Keep it inefficient to put spam into the blockchain

(see 1)

4) Filters are necessary. Not only is it more difficult/inefficient to put spam into the blockchain (as you mentioned) the other thing is that the community gives a signal to all participants that spam isn’t a use case of Bitcoin. Acting against may result in loss of reputation (social costs). Spammers should have to use inefficient loopholes to put spam into the blockchain Its only a burden if people are using the pubkey method considerably.

6) Make mining decentralized and this won’t be the case I guess. Also the profits of Mara with its slipstream service is low from what I have heard(not sure). So will there be an incentive in the long run? And you have to consider the loss of reputation a miner will suffer from doing things that Bitcoin is not designed for. Will they really do everything just for short term profits?

Don’t update, make a statement to the core team not to force controversial changes into Bitcoin. If in the future the Blockchain is flooded with fake pubkeys lets reassess.