I'm reminded that in the early 2000s it was announced with some fanfare that the UK had decided to pay extra to pursue a flexible design for what was then CVF, so that the carrier could be converted to cats and traps if needed. I think we all remember how that turned out - it seems no-one thought to write into the contract what that actually meant.
I can't imagine the Japanese ballsing things up in quite the same way, and anyway they're not talking about converting it to CTOL...