I'm not a sports watcher although I'll play sport (currently masters hockey moving towards lawn bowls(!) but also considering other possibilities).
I mainly do it for fitness as I'm Diabetic type 2.
But one of the problems with a wholesale MLS and UK competition would be distance - namely the Atlantic Ocean plus the width of the USA eg. NY to LA.
In Australia, which is not a world leader in soccer (Rugby League and Aussie Rules attract the most attention), our top competition is the "A-League".
en.wikipedia.org
A-League Men is currently contested by 12 teams: eleven from
Australia and one from
New Zealand.
There are only 12 clubs in the A-League at the moment, although there are probably hundreds of local soccer clubs around the nation.
Eleven are from Australia and the other is from New Zealand (Wellington-Phoenix).
Of the eleven in Australia five clubs are clustered relatively close to Sydney, three close to Melbourne with the other three being one apiece in Brisbane, Adelaide and Perth.
An away game for Wellington is over 2000kms, Perth is even further except for an Adelaide game, and Brisbane Roar have a lot of travelling to do.
So if you were going to have an MLS / UK competition, you'd need to reduce the number of clubs for a start as you couldn't fit them all in. You'd also have to decide if you were going to jettison the home grown competition in favour of a select competition.
We occasionally have US sporting clubs visit in Australia but i'm not sure about soccer. I remember years ago reading about the California Bears Rugby Union team having a "friendly" match in Australia (if Union is ever friendly - the NZ All Blacks don't seem to think so). I think our blokes had difficulty dealing with the long Grid Iron passes the Bears used as most of them had played that sport at some time.
It appears some US soccer players see the Australian comp as a means to gain experience for bigger things.
Talented American soccer players are finding a lack of opportunity at home due to limited second-tier competitions, so they're choosing to establish their professionals careers in Australia.
www.abc.net.au