Who would win?
Way back I read the first 15-20 books and then a few of the last ones. Somewhere during the in-between time he became more of a demi-god. Having trained in the greatest martial system that every other one was based on he should have been above Shang chi pretty early on however I do not believe that would have been the case. During that period Shang was really a match for especially when using his chi punch or kicks. Chiun is a different story of course. He was presented as being a level quite above human peak standard. I really don't remember that being put too the test very often.
Early to mid Remo can be beaten by Shang but after that Remo is just too much for him. Probably no fighter with less than at least low super human abilities stands a real chance. Maybe someone like Danny Rand hitting him solidly with the iron fist might-and I stress MIGHT sop him.