I read that in order to access the PS4 with the Vita, it needs to be in Wi-Fi vicinity and only "specific" games (which it shows on the front of the PS4 game covers) if it's compatible. However I also read they will be allowing a ton of games soon to be ported from ps3 to Vita as well so this is def. a direction Sony is headed in.
To play your PS4 games online you need a PSN plus membership anyways and if you have that, there's a ton of PSN plus Vita games each month that can be downloaded to your Vita at no additional charge.
I'm 50/50 on weather to pick one up or not, I mean the WiiU controller has a screen in it that let's you play the WiiU remotely so pretty much same thing Vitas/PS4 are doing together. Personally id rather be sitting in front of my big screen playing my PS4 with surround sound however for those players who need to be somewhere else in wi-fi distance of there PS4's this is your answer.
I also read they are planning to introduce a Vita / PS4 bundle for the holidays, the same price as Xbox one. That's not bad at only extra $100 for a Vita. I saw a bunch of new ads for the Vita at $159 though, so the Vita price is def. dropping.
Hope that helps..