With every successful and popular movie, there are always theories. Often times, fans come up with certain theories about some characters. For instance, fans had theories about Max in Fury Road. One theory was that he was actually the Feral Kid from The Road Warrior. The only thing is that there are a lot of pieces of evidence that go against this theory. One theory has recently been thrown around. This theory is that Cable is actually an older Wolverine. While at first glance, this theory might be rather strange, there have been comic stories where Cable was actually a future Wolverine.
In the X-Men movie universe, Wolverine has died in Logan. However, one thing that has been stated about the production of Logan is that the story takes place in a future time of an X-Men universe. Meaning that it is not necessarily a direct sequel to Days of Future Past. One thing that Marvel and X-Men are establishing is the idea of multiple universes. Therefore, Cable may very well be an older Wolverine in Deadpool. This can also explain his shorter stature than in the comics because Wolverine of the comics is supposed to be rather short unlike Hugh Jackman who stands at least 6’2″.
As of right now, there is no telling which direction they are going to go with the Marvel characters. A lot of people are saying that the version of Cable that appeared in Deadpool 2 is very close to the future Wolverine version. Also, Josh Brolin has the presence and the intensity to play a role as Wolverine. Either way, this is a very interesting theory that they may or may not explore in future films.