As Killjoy pointed out, this is essentially what the National Wrestling Alliance is all about. While the NWA is still around, it's glory days are several decades gone and it wasn't as though the promoters who made up the NWA were best friends forever since most of them would scheme, plot, double cross and do pretty much whatever they possibly could to enhance the financial status of their territories at the expense of each other.
Arguably, the real reason the NWA managed to survive was because of Sam Muchnick. He was the only one that damn near every NWA affiliated promoter trusted and without him as NWA president, initially, from 1950 to 1960, the NWA would've crumbled. When he stepped out of the office, all the same old problems between the promoters started rising up again under the next three NWA presidents of Frank Tunney, Fred Kohler and Karl Sarpolis. While most of the various NWA promotions, or "clans" if you will, were always sorta scheming against each other, Muchnick was able to keep everyone pretty much as close to being at ease as possible so much that they all practically begged him to take the presidency again, which he did from 1963 to 1975. When he stepped down for good, the NWA managed to muddle itself along for the next few years before Bob Geigel and Jim Crockett, Jr. began ruling the NWA beginning in 1978. By the very early 80s, a number of promotions were starting to go under, the WWF would begin its rise after Vince took over from Vince, Sr., cable television and syndication were becoming much more easily available and the NWA concept in & of itself was pretty much dead by 1985 as there were only a few strong NWA territories left.
As I said, the NWA is still around and has around 30 active territories with the vast majority of those being very small scale. They don't really have the same sort of issues now as the past territories because none of them are powerhouses. For all intents & purposes, the NWA is an affiliate of small indie territories that are really only relevant because of the past glories of the National Wrestling Alliance.
New Japan, TNA, ROH, AAA and GFW joining together is going to have major problems, pretty much the same ones as the NWA had during its time. You're going to have some within each company, not necessarily the owners in each situation but certainly executives, who feel that they're the ones who have the most to offer and bring the most to the table. For example, New Japan is the largest, oldest and most overall successful so you know some from New Japan and possibly even some within other companies, are gonna feel that they should have more prominence. On the other hand, you may have someone in AAA who feel otherwise and have a large Hispanic audience. Some TNA officials might feel that TNA is the one who should lead things because they're the ones with the strongest foothold in the United States and who've gone up against WWE and so on & so forth.
Like JK also alluded to, they're going to have to work together for the overall common good and that's just unlikely to happen. You've got too many egos involved, too many people with different ideas on which way to go, different opinions on who should be booked to look more prominent, different ideas on who should be pushed and how said wrestler(s) should be pushed. Of course, they could always sit down and come up with some sort of bylaws for the organization as a whole in which everyone has to follow and agree too, which in & of itself will take a lot of time because you'll have debates, shouting matches, compromises, etc. Even if they did manage to come up with some such bylaws, how long is it going to be before someone breaks a rule, even a minor one? When that happens, and it will, even if it's just a minor infraction, it'll probably set things off to where some will act like it's a huge deal, some will brush it off as though it's nothing, etc. Eventually, it'd probably get to the point where someone would finally push someone else too far, said someone will throw his/her hands up in the air and say "You know what, fuck it. I don't need this shit. We were doing just fine on our own before." All of these companies, with the exception of GFW, are high profile in their own way: New Japan Pro Wrestling is the 2nd largest promotion in the world, AAA has been a powerhouse organization in Mexico for well over 20 years, TNA has been the largest promotion to come along to national prominence in the United States since the demise of WCW and ROH has been pretty much the undisputed King of the Indies since the mid 2000s. That breeds ego and personal brand loyalty that's difficult to put aside. Working a few joint cards here & there is one thing, uniting under essentially a single banner is something else entirely.
IF they could come up with some sort of bylaws that they could all live with, IF they could find someone in which they all trusted to look out for the interests of everyone involved, IF they could have someone to have the final say who would be able to at least satisfy everyone just enough to hold things together; then it MIGHT be something. The odds of it happening in this day & age are just not good at all.
