Where talking about Sega, a company that had a hit with Valkyria Chronicles on PS3 , then did the the second one on PSP and the third never left japan .

Japanese weren't buying the Wii U either before compelling titles came out or were announced. Your argument is moot, and only a way for you to downplay the PS4. 

Again Japan =/= the West

The situation in the West is very different, the system was extremely hyped from the start and it actually already has the biggest western games, albeit they are cross platform but still.

In Japan, the system launched with way less hype and almost no compelling software for the market, that is why sales are as low as they are, that and the console market in itself is just shrinking over there.

But the conclusion you're arriving at just isn't all that rational, just because the console has a slow start, does not mean it'll never pick up.

do you think the 3ds could get a port?

Why 3DS?

why not, It is getting Persona Q

don't you think it will sell?

the 3ds is the best selling system at the moment

That's not saying much.

maybe a 3ds/Vita port

It´s simple, the 3ds sells a lot, that´s right. But the sistem doesn´t have enough ´´power´´ to run a Persona 5 port and the vita would run it without any problem. P4 golden sold a lot, so I think that the port will be for vita.

Every Persona game has at one point or other been ported to a handheld. Atlus doesnt seem to care if the handheld in question is winning since P1-3 were on PSP with a 80mil base vs. the 150mil DS base, same went with Persona 4 going from PS2 to PSV instead of 3DS/PS3.

Based on what Atlus has done in the past, it makes most sense and thus is most likely, that the game will be ported onto PSV again, possibly a scaled down version of P5 for 3DS similar to P3P at the same time period will be released. And P5 may hit PS4 as a port like P4 did for PS3.

Given the game is coming earlier this gen than P3/4 and with more money thanks to Sega we may see a P6 for PS4 before the end of Gen 8.