Uh...so the vita version of Dies Irae has the same release date as the steam version.
Now, about getting the game on EU PSN...
https://mobile.twitter.com/diesirae_steam/status/856340211952791552
I don't buy it, personally.
I assumed a port would happen eventually (and half suspected one was already planned for Japan before the kickstarter started) because light have experience porting their PC games to Vita - they released KKK, Silverio Vendetta, and Senshinkan Gakuen Hachimyouji already, after all. There's also the fact they already released a PSP port of DI.
That said, a vita port hasn't been announced for Japan yet, and as this PC version is meant to be the most-complete-so-far I assume there might be content in it that might need pruning before a Vita version could get released.
If it does, that means the translation might need alteration to accomodate for that. Then you need to get someone to actually apply the translation, and maybe re-code to allow the correct amount of space for it. Then you need to get it rated.
Then
even if that was all done, this is a company that can't even get their physical PC prints done on time because of... whatever reason that ended up being.
I don't think they're capable of releasing a Vita version on the PSN without experiencing problems.