potentiultimate
Possibly the last; potentially the ultimate.
Since they are building a new apartment building in between this one and the Space Needle, this may be the potentiultimate New Year's Eve party at my place if it ends up being too tall.
Potentiultimate
Potentially penultimate; potentially the second-to-last time a given event will occur.
Because a huge new apartment building is going up between Derek's apartment and the Space Needle, he invited all of us over for a potentiultimate fireworks show this New Year's Eve.