Re: D3 on May 15th!
Already pre-ordered through a national game store chain shortly after the collector's edition was announced. Now I just have to hope that location's doing a midnight release.
I'd say it'll likely be out on consoles; they've made it public knowledge that they're hiring console people, but haven't yet come out and said, "Yes, this WILL happen."
D3's longevity will suffer, I think. You can still plan builds. However, due to how skills/runes unlock as you level, you might not get the runed skill(s) you really want until you're nearly at the max level. There will be optimal ways to play character classes until you get to that point, so if every character you make will be cookie cutters for the majority of the game then there's no real "newness" to making new characters. It comes down to how happy you are to respec your characters & if you want to level new ones.
Plus, the items aren't really known. We have no idea how much desire there will be to do hundreds/thousands of runs anymore. Plus, with the auction house you can potentially get the exact items you want without putting in any of the effort of actually FINDING it; all you need to do is level a character, buy your gear, and that's it.
edit: Perhaps my viewpoint of D3 is shaped by D2 too much, though. Maybe now build planning isn't focused on the majority of the game as it was in D2, but instead build planning is linked mostly to Hell/Inferno only. The challenge lies in creating viable builds that can make it through the hardest difficulty. Maybe this excercise is enough to give us enough challenge to keep us playing the game for years.
Time will tell how long we'll be playing.