The Weapon X program was the experiment that turned Logan into Wolverine and what he went through there has been a key part of his character since the first X-Men movie.
The first Wolverine standalone film X-Men Origins: Wolverine dealt specifically with the events of the Weapon X program, however, that film was viewed as one of the weak links in the X-Men franchise to date, and its events were essentially retconned out of existence following X-Men: Days of Future Past.
Naturally, calling Wolverine 3 Weapon X also forges a connection to the type of cameo that Hugh Jackman filmed for X-Men: Apocalypse.
What do you think of Weapon X as the title for the final Hugh Jackman Wolverine movie.