Seems like DQI is free if you get the true ending in DQXI in Japan.I wonder how the Switch version will be like - if its like the 3DS version except with better visuals, Ill get that than the 3DS ver.
About the DQXI on Vita discussion I can say only that the 3DS version was made to Japan only where 3DS matters a lot... só SE was smart and it won't probably be localized to west.
PS4 (Japan/West) and 3DS (Japan) makes perfect sense with Switch (Japan/West) port late for double/triple dipping.
Vita version should fail hard... so SE didn't even bother.
As for myself, I'm planning to buy the PS4 ver.