Nope 1080p is the highest quality you will get on the NowTV App with the additional Boost Pass.
The drawback using the LG native NowTV App is that 50fps in not currently available on the LG Smart TV's so you won't get the super smooth playback on the Sky Sports Main Event, Premier League and F1 channel which in my opinion is a must for watching sports.
Further information can be found in these two NowTV guide articles linked below.
I know its a pain, and a bit defeatist... but NowTV are spread way too thinly on the platforms they say they support.
Therefore we are in a position now where not all platforms are created equally.
As another poster has mentioned, you wont get 4K although your TV probably does a nice job at upscaling anyway.
Best you can hope for is the 1080p BUT thats only through platforms that support it, and there aren't many of them. No idea if they do so on your TV but theres a webpage where they detail what is supported.
Sadly, back to the defeatist attitude... your best bet seems to be the NowTV Box or Stick... as those always are the most up to date with functionality etc.
Ironically, and quite on subject.. the NowTV box is a 4K box... but NowTV itself isn't a 4K service - so the 4K stuff would only be Netflix I think.