I pondered the same question in my TR, unlike the original versions these ones have been dubbed over in Japanese so the lips don't really match up so its not like they need to re-film the actors, I wonder if they really want to keep it if they will just re-record the dialogue and update the dashboard on the deloreans to read 2055 instead. Since the dashboards change every day to show the current date changing the future date and changing the lines of dialogue that mention 2015 shouldn't be too expensive.... maybe?
I imagine it would be something like this, I obviously don't know the numbers to tell if the ride is popular or not but I am sure they could come up with a solution if they keep it.