Given the power of the StarCraft 2 editor and the long-running history modders have with Blizzard games, the only disappointing thing about this mod is that it didn't come to life sooner.
It's called WarCraft: Armies of Azeroth, and it's a fan-lead project — much like the remake of the original StarCraft and Brood War campaigns in SC2 — to remake WarCraft 3 in the StarCraft 2 engine.
An alpha build of the mod has been released for all and sundry on the StarCraft 2 Arcade, with the creators asking fans to hang out in the #warcraftforever, #warcraft4plz and #warcraft_aa channels on Battle.net if they want to chat or pass on feedback.
If you want to try out the alpha build, simply search "WAA Turtle Rock" after clicking on the Arcade tab within StarCraft 2. More progress on development will be posted online through their ModDB summary as well.