i think you have your hopes set way too high, this is just a remaster of an old game by a small team, all of the visuals are being outsourced to another company and not actually done by blizzard, so i doubt they will be doing any major campaign DLCs.
If they were to make a new campaign it would probably be best to make a new engine that can support enhanced features such as co-op, since thats much more popular these days.
In order for a company to further develop DLC the game must have a large player base which currently wc3 does not, but will see if reforged sparks interest in further development which will probably go into a true sequel since they would be able to do more with DLC in a new game