I have no objections to adding a rect function - and I am perfectly happy to do it for the next update, but I think there is something
The PPU on the other hand is a completely arbitrary made up by Unity. You still need a camera thats set up somehow, and for consistencies sake I assume you'd use the same pixel per world unit value everywhere in your project. Do you tend to use different ppu values for different sprites for unity sprites?
I need to find a way to calculate current displayed pixel size of a sprite that won't be dependent on the screen resolution.
This implies you just need your "constant" ppu that you're using throughout the whole project, the world space bounds * that constant ppu value will be your "pixel size". In fact the world space bounds will be constant as well, you don't even need to multiply by ppu to position things, the world bounds and positions work just fine.
That is my main issue with the pixels per unit value in unity - all it says is how big the sprite is. It has no bearing with actual pixel size, or how many pixels it maps to on screen / world space.
I may be missing something crucial here... please explain if you can, use the support email if you prefer. If you can send me a repro case I will be more than happy to look.