No issues - I did a conversion like that myself on an ebike. It required respoking the front rim onto a disc compatible front hub - I used a DH model. The fork was replaced with a disc compatible Rock Shox and the installation went from there.
The only reason you might NOT want to do something like this is if you use the rear brake more than the front. Believe it or not - some people do that. Otherwise a V-brake or canti in the rear will provide more than enough force to lock up the rear wheel when its been unweighted by applying the front brakes.