I thought of this a long time ago.
Surprised nobody makes one - yet!
Doubt it will be long before welding helmets use a screen and a camera like a VR headset.
Will make it much easier.
I tried with a phone held inside the helmet but it wasn't too great as it was constantly trying to self adjust.
I also tried with different lenses, fixed shades etc and tried an older digital camera and none were very good.
In the end I got the best result by using an IP Spy camera glued to a pair of old specs but it was quite hard to get the camera looking at the right point.