Hi Res Font?
 

I've noticed when i try to scale the UI in either direction the fonts on my quest tracker start to become unreadable would it be possible to replace the font used by the standard UI with one that might scale a little better?

There's no way to interact with the font at this time by the modders and I don't think it's high on Turbine's priority list either (although if more and more people start asking them on their forums it might be added some day).

Only font you can scale up is the chat box fonts from the game options I'm afraid.

Yeah, and you can change the sizes of the floating text in the game. One cannot change the fonts of the UI.