Is it within code to leave unused romex wire within a stud cavity for future use?
It is fine to do what you propose, as long as you are 100% certain that the cables/wires are not terminated at the feed/switch ends. This is very common. This is NOT burying a junction box or splice. There is no code prohibition to leaving a dead wire in the wall for future use.

I would however take photos of the area for your own records, and label the ends of the wires at the switch boxes just in case you don't follow through with this and the next owners find them. They may want to do the same and have a pleasant surprise.