I don't believe Japan has even done a study to flesh out the requirements for a 6th generation platform. It sounds like what they're really trying to do is to get started on some technology research so that they can pull the US in for joint development.The ATD-X, to be flown in 2014, will demonstrate some of the technologies intended for the F-3. Full-scale development would begin in 2016 or 2017 and the first prototype would fly in 2024-25, according to the ministry's plans. Series production is to begin in 2027 and the type would begin replacing Mitsubishi Heavy Industries F-2 strike fighters in the first half of the 2030s
the japanese are not working on a 5th generation fighter but a 6th generation one why?
Japanese participation in the next U.S. fighter program is now conceivable because Tokyo has relaxed its arms-export restrictions, which in the past have largely prevented its industry from working with foreign partners. The way is not entirely open for cooperation, however, since Japan might be reluctant to supply some countries that the U.S. sees as suitable customers
plus the article says
The ministry also wants to push ahead Japanese ECM technology, to preserve national independence in that area that was developed in building a system for the F-15. The ECM work must be part of what the ministry calls an “all-around surveillance and jamming system.” Japan is also looking for “reflection suppression” technology, apparently distinct from stealth shaping and materials. Details are unavailable. Results of this electro-magnetic work are to be assessed in 2019.
Other work flagged for the i3 Fighter might be enticingly dangled under the Pentagon's nose, though. The Technical Research and Development Institute and industry are working on skin sensors, directed-energy weapons and advanced avionics
Paper airplane accusations aside (since that's what they used to say about the J-20 too), this thing won't even begin prototype testing for a while. I doubt it would be put into production in time, and by then China could very well be developing their own next generation fighter.