But that was not the argument with which this feature was justified. It wasn't "we can forgo replay protection with this" but (among others) "we are even helpi

But that was not the argument with which this feature was justified. It wasn't "we can forgo replay protection with this" but (among others) "we are even helping the hardforking side, during the BCH hardfork many BCH nodes connected to BTC nodes and couldn't propagate their transactions". But as long as the hardfork hasn't happened, there is no reason to do this. This just makes signalling even less useful than it already is because nodes will be encouraged to lie about their intentions.