Does anybody make a Savage-style barrel nut for a Remington 700 ?

This would allow the mass making of swappable barrels like is happening for the Savage 110 family.

How hard would this be for a skilled machinist to make ?

Hammer

Not very hard, I've seen a couple versions of this, one with a large hex nut, another with a castle-type nut. It would facilitate the barrel change out, but I'm not sure you would get anyone to jump on the bandwagon and offer pre-machined barrels for it. I could be wrong tho'. - Dan

The Savage and Remington might use the same threads IIRC. Something worth checking out.

Remington and Savage use a different thread. The other thing that you must think about is that the Savage doesn't have a recessed bolt face like the Remington. On a Remington both the bolt head recess and the action/barrel shoulder have to be set up just right. Also anytime the action is remachined you'd screw up these relationships. Because of these issues the barrels would have to be set up for a particular action i.e. action and its mateing bolt.