After World of Warcraft released and quickly became one of the most popular games ever, I figured that it wouldn't be too long until Warcraft 4 was released. After Starcraft 2 was announced I lost hope in a Warcraft 4 release as it didn't make sense for Blizzard to push two strategy games at once.
That said, I...

I believe this is the first I've heard of Warcraft 3. I obviously live under a rock in the middle of no where. I might have to look into it. I played the first two games, but have never played WoW. As for SC2: LotV, it seems to still be in production according to Wikipedia (http://en.wikipedia.org/wiki/StarCraft_II:_Legacy_of_the_Void), although it's been about 10 months since it's been updated, so hopefully it shall be completed soon.
I think Starcraft 2 was more important to get out, and I'm glad they went that route before going back to Warcraft. Starcraft 1 is a bit of a chore to play these days, while Warcraft III is still as good as ever.
But yeah, I think it's time for a new one. I'd be surprised if there weren't some design documents somewhere already. I don't know how many teams they have but hopefully once a couple of years have passed after Legacy of the Void comes out, we get a new Warcraft.
Greg: Warcraft III was released in 2002, so if you weren't doing a lot of PC gaming back then, you might not have heard of it. At the time I was at University and all I had was a laptop for school work and no money for a console. So I mostly played PC games.
Travis: I agree as I am really excited about Legacy of the Void. Hopefully it's not as long in the making as you say, but what you say sounds right.
Yeah, i was at "University" at that time, too. I didn't do a lot of PC gaming, mostly console gaming as I had all three current-gen consoles at the time.
It'll be interesting to see how/if Warcraft 4 shapes up. I wonder if the current emerging esports scene will influence the game. Especially considering one of the major esports games is an outgrowth of Warcraft 3 (Dota2).