How to Make a Bow-Kata Monk/Fighter?

[Misterwhisper]

That was a spell in PF, at least, that let you use a bow as a quarterstaff.

Come to think of it, that might work alright for 5e. They could just base it off of Shillelagh, and go from there?

I would just make an uncommon magic item, bow staff.
Command word to change it from a bow to a quarterstaff.
No magical enchantments come on it normally but it can be enchanted later.