Just because Liev is back, how do you avoid not falling into the same clichés of Origins? Brothers reconciling their differences and coming together to face a greater common enemy would be repetitive, and they shouldn't go there again. Will they even be in Vietnam together in a new timeline following 1973? So that alone may eliminate another rehash of Victor Creed. Far as Deadpool, I think they will stay far, far away from the Barakapool version we got and instead emphasize Wade Wilson in X-Force.
First and foremost, we have to see where the character is at following DoFP before we can make assumptions on whether it makes sense for the character to return. If Logan succeeds in repairing the timeline, his mission as an X-Men may be done and they could leave it at that before essentially rebooting the character in the future.