The original agreement was to reduce the 22 PL teams to 21 and then to 20 in the first two years. The reduction to 18 was agreed upon without any time limit, so we are still waiting for that sensible change.Regards the structure of the top league....obviously it be governed by finance and profit.
The English Premier league is by far away the most popular league in the world with the highest revenue, just over double the nearest challenger (La Liga). So as things stand there's zero chance of any club wanting to leave the Premier League.
What is likely to happen is
1: The Premier League cuts down from 20 teams to 18 teams, like many of the other top European leagues.
2: We'll see the experiment of official league matches taking place abroad, especially in the US and possibly Saudi Arabia.
Apparently FIFA have just given the go hard to allow this to happen.
3: The UEFA Euro leagues will be expanded...so the top half of the Premier League will be playing several European matches each season.
This means those clubs won't be able to play in the EFL cup and those clubs might even forfeit the FA cup too.
4: A large spread of kick-off times, so most people can watch live Premier League matches continuously from 12 noon to 7pm on Saturday and Sunday every weekend. Basically the regular 3pm spot will be a thing of the past.
If the Euro league becomes excessively popular...more popular than even the Premier League....which I doubt.
Then I suppose in 15 to 20 years....it is possible the big European clubs might get together to form their own league.
However remember that UEFA are aware of the breakaway threat so they'll be making efforts to make their format more attractive to most clubs.
A breakaway Euro super league would be a massive risk because the respective domestic leagues would banish them with no chance of a return.
So don't think this would happen. Think it's more likely a deal might be done with the Premier league to reduce the PL fixture list
and have a Euro super league running side by side the domestic leagues.