Personally i think that it really depends on weather oda finishes the World Government stuff before or after Laugh Tale.
Like if oda has Luffy go and fight the marine admirals first then the last arc would be vs Blackbeard for the one piece, but if he has them go after the one piece first then the last big fight would be vs the admirals and other World Government people like Im.
There's also the fact that a few of the dreams of the crew that aren't finished with finding the one piece but some that are, i.e. Robins dream is to find out everything about the ponaglyhs which lead to Laugh Tale.
Personally i wish for one piece to go on forever but that's unrealistic sense we are already 25 years in and it seems like its getting close to the end.