If Elon is to integrate crypto payment into X, I personally think it's not going to be any other coin other than dogecoin.
I don't know about any X coin have that possibilities, but the entire crypto space knows that Elon musk is the reason why dogecoin is where it is today, without Elon, dogecoin will probably be buried somewhere in the top 300 to 400 according to coinmarketcap, this is judging from how far alot of coins with better technology have developed, dogecoin have no technological backing, it's just a hype coin, and Elon brought dogecoin and made it sit at the top 10 in crypto currencies ranking according to coinmarketcap, I do not think he will abandon it now, so, if ever X is integrating a crypto payment, I think dogecoin will be the number one choice.