The KHL (Continental Hockey League) has teams from Russia, Kazakhstan, Belarus, Latvia, Slovakia and Czechia. So there aren't any logistical problems that can't be overcome if the finance and willingness is there. They play more games than football teams yet still manage to have a team like Khabarovsk play away to Prague (they're eight time zones apart).
That said, there's really no need for multi-national leagues in football and I imagine there'd be very little support for the idea from fans.
Sigesige00, you say Welsh teams would leave the English set-up to play with Scots and Irish teams. Why on earth would they want to do that. Another point: you advocate an Austrian-Lichtensteinian-Swiss league. All Lichtenstein teams currently play within the Swiss pyramid, so we're nearly there.
I know this is very off topic, but it's interesting you advocate the return of the USSR. Go to Bukhara, speak to an Afghan war vet and ask them if they want to be ruled from Moscow again, ask a resident of Karabakh if they want to be in the same country as Azerbaijan.