Couple of issues with this approach.
1. Most of the teams talked about already play in such a league...its called UEFA Champions League. Yes there are relatively weak teams in UCL from the smaller countries. One simple answer to me would be to change UCL to be similar to the League of Nations where they have different divisions. Just put the super clubs in the upper division.
and the big one
2. I suspect that if these clubs were to pull off this FIFA would revoke their memberships and keep them from FIFA sponsored events. And FIFA holds a huge hammer here. They could say to these clubs fine you have a right to do your own thing but your players are no longer eligible to play in FIFA events...so they can't play for their respective national teams or in the World Cup.