From another forum: "They wouldn't be allowed to play a league between the 2 jurisdictions, the very most they could play would be a non affiliated cup/"
I'm no expert (understatement!), but I'd say that is correct.
Even in the case of individual clubs seeking to play in another country/jurisdiction, there needs to be a pressing need, or historical precedent, before the respective Associations and FIFA/UEFA would consider it.
While cross-border competitions between teams from different leagues may be permitted (eg Setanta, Baltic, Scandinavian Royal League), an actual merged league throws up much greater issues - see eg UEFA's absolute opposition to the European Super League.
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