Why would the football world be more tied to major metropoli in the future? I think everything that is happening in football suggests that the local stadium part of the football business will be less and less important. The global brand will be the decisive factor. For most fans already, Manchester United is essentially not a club out of some shithole town in Lancashire, it's a carefully developed fan experience designed to look good and sound good. With VR viewing, that's going to be even more important.
Then the question is, which club brands will be the most important in 30 years? Well, take a look at the most recognized clubs from 30 years ago. Not that much has changed, really. So far we haven't seen a single newly founded club become truly globally recognized. Los Angeles Galaxy probably comes closest, but it's still a tiny club on a worldwide scale. Sure, clubs like Milan, PSG, Chelsea and Manchester City have become powerhouses because of heavy investments, but all those clubs already had an extensive established fanbase to begin with. RB Leipzig is of course the one potential exception in this, it will be interesting to see how their development continues.
So, anyway, if there is a successful international super league in 30 years, my guess is that it consists mainly of West European clubs, almost all of them owned by foreigners. Probably Asians from whichever part of that continent is running a financial boom. Forget Kolkata and such, Villareal has more chance of being included.
Irriducibili? No thanks, I'm a fan of Lazio.