I was thinking this exactly. Not much of a problem for data, more of a problem for display of the data. A good stop-gap until they get enough information about the new era would be to just display the dates in UTC for a while or something.
I mean, unless they're storing the date/time in the database as a string, formatted for Japan's locale. Then they're screwed, kind of. I mean even then, it could be fixed with a stored procedure within an update statement.