the vastly improved world editor will be a huge boon, not to mention other behind-the-screen upgrades like matchmaking anti-cheat etc etc.
What is great is that its the same war3 engine as from 2002 (just upgraded) and that its all compatible with war3 classic (melee and customs).
Another point is that the dev stated all the old audio and video assets from war3 classic will be in Reforged, so we can probably switch what we want to hear/see just like in Starcraft 1 remaster.
I am guessing that with the release of Reforged the classic war3 will become free of charge, and with some reasonable cosmetic items Reforged might have a stable financial income that supports further patches and developers.