it's been a topic/speculation/stated in no uncertain terms since the X purchase: Elon wants to add payment functionality as part of his goal to make X the "everything platform." 

X will launch peer-to-peer payments in 2024

this market will resolve when P2P payments are fully available to users (even as a premium subscription service) - not in a beta/testing phase. the service must be rolled out across at least one entire country (I'll duplicate this market for international payments, in case the launch is handled separately for any reason).

official announcement/mention in a post on the twitter blog

separate market for the launch of international payments across 4+ countries with different primary currencies: