Just a couple of years ago, it would have been unfathomable to think about WWE even mentioning another active promotion.
Now they have a working relationship with EVOLVE, they continue to work with top talent while they continue to work with independent groups, and there have been talks about tier pricing on the WWE Network that would include wrestling from other companies. At one point, there were talks about adding Progress and ICW to the network but that has yet to happen because Vince McMahon changed his mind and it’s been years since those talks started.
However, there is another idea being talked about internally for 2019. Dave Meltzer of the Wrestling Observer Newsletter reports that the idea is to run a WWE Network special featuring talent not under contract. This could open the doors to work with other companies and they could also use talent from groups they currently work with such as WWN Live, ICW, and Progress.
Again, that is the idea but it could always fall apart if Vince McMahon changes his mind.