I've been asked to arrange approval of a few nosewheel brake mods on various light types, and they are invariably a pain in the neck.
(1) The main aircraft structure is seldom designed to take what in effect are compressive loads towards the middle of the aeroplane.
(2) If used at speed (landing or aborted t/o) a nosewheel brake alone tends to destabilise the aircraft and it can try to skew off the side of the runway.
(3) Mains already have a very substantial structure that doesn't struggle to take braking loads, this is not necessarily true of noselegs which are much lighter affairs.
(4) You can't achieve differential braking with a nosewheel brake!
(5) Trying to put significant braking effort through one or two smallish tyres (the usual on nosewheels) leads to very short tyre life.
So it's possible, but in general terms a daft idea best avoided.
G