If they were to have an RTS team work on upgrading the SC2 engine, it would be fairly easy to remake WC3 in a more.. sane... way than Reforged. As there will be no custom maps to start with, people will not complain about any compatibility breaking features and so they would be free to get rid of all the annoying aspects of Warcraft III without concern.
That said, they might as well just make a Warcraft IV then. Would cost about the same to develop...