It probably wouldn't follow the path of Arena. Arena is a fighting game series which perform decently on Xbox. RPGs do terrible on Xbox. The audience just isn't there. It really depends on how the PS4 performs in Japan. If it's performing worse than the Wii U by 2016 (the earliest I think a remake would come), Japanese devs will not likely move there for games unless they think Western sales can cover for it. They would stay on Handhelds and the biggest profit would be on Nintendo's handheld. 

Could PS Vita users play SMT games like (DDS) then since you want Persona 5 on the 3DS which would be a downgrade.

I really don't want Persona 5 on Nintendo hardware to be honest. I feel as though not only will it make the costs of developing the game go up more since your developing for multiple platforms, but I just do not believe that the audience is there. Sure, Persona Q might sell decently, but the sales will be no where near Persona 4 on the Ps2. Also lets be honest, non-Nintendo games most of the time never do that good on Nintendo systems.

It could happen, but i'm skeptical. I see Persona Q as being a lot like those Final Fantasy spins offs on the Wii; a consolation prize for a platform that will never get the main entries.

No Persona game will have sales near Persona 4 on the PS2.

I think that Persona 5 will exceed 1 million sales and be the highest in the series.

of course seems doable.

Did you read my opening?

I think that if P4 couldn't do it on the most successful console in the industry with a 150m installed base, P5 doesn't have a shot with an 80m installed base and a weaker presence in Japan.

Looking at Monster Hunter I disagree. Also look at SMT (for the fanbase argument). 

Lastly Persona Q is going to do extremely well for a spinoff, dont be surprised when it outsells most of the persona games and gets very close to the Main ones (might even surpass most) :P