Most Unity-based games I've seen have UI scaling, so one would think it wouldn't be too difficult. Pillars certainly has some text scaling, which is great, but the icons need to scale, too. On my 27" 1080p display, the main UI icons are just way too damned small.

 

This is what the UI looks like now:

 

 

Notice how each UI icon is about 1/4 the size of the portrait icons? Yeah: they're super tiny. Ideally, I'd want the icons to be about this big:

 

 

Now doesn't that UI look much easier to navigate?

They look about the right size to me on my 13" laptop at 1920x1080. Can't imagine how big you must be wanting them if you find them too small when stretched to 27". The good news is that this is moddable, though obviously it's too early for PoE mods to be very numerous. Google for the Infinity Engine UI mod - they've added some UI customisation. Now I don't think they've added the kind of resizing you're looking for, but the mod might give you some idea of how to switch out the icons for bigger ones.