Probably won't happen: Crossover with New Japan Pro Wrestling
One thing seems crystal clear: New Japan Pro Wrestling does not seem interested in a working relationship with All Elite Wrestling.
For one thing, NJPW sees AEW as direct competition. Indeed, many of their top stars have already signed with AEW or are direct founders. For another, New Japan Pro Wrestling already has a working agreement with Ring of Honor, and the two promotions seem to be happy with their arrangement.
This isn't to say that some AEW wrestlers won't work dates for NJPW or other promotions, but that there won't be a formal exchange of talent between the two entities. This means that, for example, Chris Jericho might wrestle for both AEW and NJPW, he won't be defending titles he won in All Elite in New Japan, and vice versa.