I’m not entirely sure. In the western app ecosystem it seems that the only dominant app present in almost all user phones are the ones by Apple or Google themselves. If they choose to get into the app game in a big way it could be them. After all, they are well poised to dominant the mobile wallet game. Links to payments is essential.
Alternatively, it might be a dominant ride-share app like Uber or Lyft.
Social media is a close possibility. Maybe Facebook may not do it under their core brand but start another branding and team. Or it could be a e-commerce giant like Amazon or Paypal.