So it's a given that this will never happen but let's say hypothetically the WWE were to strike a deal with another wrestling company ala UFC and Invicta which would make the most sense for both companies?
ROH: still a somewhat dedicated fanbase who might plop down money to see them on the network and they're small enough that even Vince wouldn't be paranoid they would steal his spotlight. On the other hand it's similar to Invicta that if you're a fan of ROH you probably have the App already, also ROH doesn't need it because they basically cost nothing at this point and are owned by a media distributor.
TNA: About to get dumped by their distributor (probably), enough name talent to draw some buzz and get numbers on the network, but WWE wouldn't pay enough for the content to keep them afloat and Vince would want to bury them into the ground just because he's old and cranky and he hasn't done it in a while.
Have a good one,
New Japan, by far. They've already poached Devitt and KENTA and it would actually work as an alternative for guys to work when they need to freshen up. We've all been saying for ages they should just get the rights to some of the shows from last year, re-dub them, and show them on the Network. Wouldn't make a lick of difference for subscriptions, but it would be awesome for the future of the company and help to boost NJPW's standing.