I think the question should be how to coordinate so Bitcoin has (more) layer one privacy and fungibility.
All that Bitcoin cares about is that in each block all transactions are valid. “Nothing” stops us from making a single transaction per block with all inputs and all outputs arranged in a way that subset sum analysis is broken. Not the same as Monero's ring signatures, but both for good and for bad.
And then of course move as far away from the base layer as possible, because blockchains don't scale.
IMO Monero just chooses different tradeoffs and pushes the scalability problem further, but does not solve it.