Sony wasn't even willing to pay what was necessary to keep FF XIII exclusive out of Japan, what makes you think they'll suddenly start throwing money around for DQ X?

If it means Vita sales blowing up in Japan, then I would say go for it. Nintendo probbly has MH4 on lockdown, so I doubt they'll go for that. It would be risky right now, but in the long run, it should help the Vita. 

I think they're completely different situations. FFXIII came fairly late in the console cycle (2010), the ps3 had already established itself and had a fairly strong line up of exclusives, sony had far less to gain, whereas the Vita is in a far more awkward position. I'm pretty sure Sony were unaware of its multiplatform release until Microsoft announced it at their E3 2009 press conference. Also the fact that it was announced at microsofts briefing would lead me to believe that they had paid for a multiplatform release, meaning it was now out of sony hands. 

However I do doubt that sony will secure a Vita release, but there no reason why it shouldn't/wouldn't happen other then Sony's incompetence.

Yeah, squeenix has said before that DQ will always be on the most popular/best selling system.

Dont think there is any hope it will end up on the Vita. DQXI is very likely to appear on the 3DS aswell.

On the bright side, you got PSO2, wich is better than a kick in the teeth.