What's stopping crossbow sights?

I know this has been requested A LOT, but I'm not asking for someone to make it, just what is stopping people from making a mod to look down the barrel?
I have no mod making experience and only a tiny bit of programming exp, but I have a desire to learn.
A crossbow overhaul is one challenge I want to take one. It seems like aligning the crossbow would be relatively simple for first person view. Obviously in third person the crossbow would clip through the body if it was lined up, but who wants to use bows in third anyway?
The other problem I see is the crossbow would block the lower half of the screen, making targeting long distance impossible. I say that's part of the challenge, and a natural nerf to crossbows I want to make more powerful.
Anything I may be missing?