I am a 6'3" violist, and I want to know how feasible it would be to switch to violin
Answers (1)
There is no reason a tall person would have any difficulty playing violin.
On the other hand, being tall does offer a significant advantage for playing viola, since your arm can comfortably handle a larger instrument which will generally sound better than a small viola.
Why not do both? I have played both violin and viola (and many other instruments) professionally for decades. I am over 6'2".
Hope that helps.
Chris