I can just about guarantee it’ll be the Eurofighter, just like India will do the same. The Eurozone is shredding economically those countries that can’t keep up and will assimilate them later as proxy’s, extra man-power. America slides and Japan must link to a new power that’s not China or Russia, for their own sanity.
I don’t think it will be either. My money is on two different long-shots. Either they will somehow convince the US to reopen the F-22 line, which is the bird they want the most anyhow, or they will go in with Korea on the F-15SE Silent Eagle.
The second choice offers a number of advantages. It will increase cooperation between the Japanese and Korean defense industries and military forces (something both countries agree is necessary) and it gives them a platform that is very familiar in a lot of different ways because the JASDF already flies the Eagle and knows it well.
The Super Hornet is a non-starter because of its known limitations and lack of stealth, while I just don’t see Japan wanting to risk alienation from its No. 1 defense partner by choosing the Eurofighter.
The final deciding factor may be the F-35B variant, which I believe (official denials notwithstanding) the JMSDF is very interested in acquiring for its Hyuga and Ise class ships in the future.