Once Upon a Deadpool may be the last chance for Hugh Jackman to cameo as Wolverine in another X-Men movie. Jackman will always be the first actor to portray Wolvie in live-action on the big screen, thanks to his performance in 2000's X-Men. The actor has since reprised the role in every mainline X-Men sequel released over the past eighteen years (either in a cameo or as a lead), and further headlined a trilogy of Wolverine solo movies that culminated with last year's Oscar-nominated Logan. Technically, Jackman has even shown up in a Deadpool film, if you count the X-Men: Origins - Wolverine footage that was reused during Deadpool 2's mid-credits scene.
Deadpool 2 is now headed back to the big screen in December for a special two-week run as Once Upon a Deadpool. In addition to being a PG-13 cut of the very R-rated sequel, Once Upon a Deadpool includes brand-new footage in the form of a framing device where Wade Wilson (Ryan Reynolds) "reads" Deadpool 2 to a now-adult Fred Savage, whom Deadpool has kidnapped and forced to reprise his role as The Grandson from The Princess Bride. In light of what's happening in the X-Men cinematic franchise, though, it might be now or never, as far as Jackman making a proper cameo as Wolverine in a Deadpool film goes.
It's been widely reported that the Disney-Fox deal is expected to be finalized by January 2019, at which point Marvel Studios will officially gain back the film rights to the X-Men characters. While it remains to be seen exactly how Kevin Feige and Co. go about incorporating the X-Men into the Marvel Cinematic Universe, it's fair to assume that the Wolverine character (whenever they show up) will be rebooted in some fashion, now that Jackman has formally retired from the role. It's further reasonable to assume that Jackman won't be cameoing as Wolverine in either of the remaining two X-Men movies that went into production before the Disney-Fox acquisition (2019's X-Men: Dark Phoenix and The New Mutants), seeing as that would either contradict and/or lessen the emotional impact of Logan's ending. For the same reasons, Jackman won't be able to reprise his role further down the line in something like X-Force (assuming the Deadpool spinoff still happens, of course).
A Jackman Wolverine cameo in Once Upon a Deadpool, on the other hand, would be perfectly in-keeping with the meta comedy of the Deadpool movies, and further allow fans to bid farewell to the character on a more light-hearted note than Logan (without lessening that film's somber conclusion in the process, that is). Reynolds and Jackman, for their part, have been relentlessly teasing the idea of a Wolverine cameo in Once Upon a Deadpool in recent weeks. Among other things, Reynolds released a parody voter ad for Jackman's political thriller The Front Runner and further taunted the actor by calling Jackman "selfish" for not wanting to return as Wolverine. Jackman repaid the favor by releasing his own fake voter ad for Once Upon a Deadpool and is scheduled to make a "huge" announcement on The Today Show this Thursday. At this stage, it it would come as more of a shock if Jackman didn't confirm that he's cameoing as Wolverine in Once Upon a Deadpool than if he did, at some point. [UPDATE: Jackman's Thursday announcement, however, did not involve Once Upon a Deadpool.]
Of course, there's incentive for Jackman to reprise Wolverine in Once Upon a Deadpool beyond just fan service. Reynolds has revealed that for every ticket that's sold to the film, a dollar will be donated to his cancer charity "F*** Cancer" (which, in light of the movie's PG-13 rating, has been renamed "Fudge Cancer" for the time being). So really, all talk of the X-Men and Wolverine character's future in the MCU aside, a Jackman appearance in Once Upon a Deadpool would still be in service of a noble cause for the winter holidays. After all, what better way to celebrate the most wonderful time of the year than releasing a movie in which a wise-cracking assassin and an adamantium-clawed brawler learn valuable life lessons together?