Diablo 3 is not dead, the game is in a maintenance mode - something we know from one year and which was speculated even before that, when Josh M. left the team and the second expansion was oriented to become a DLC. Whether we'll see more character DLCs is unknown, but as Green said, I too prefer more in-game changes instead of new classes.
Money incoming is the only way to prevent D3 falling into a real maintenance mode as D2 have obviously done. Saying that, it is very important that there would be another class DLC. Ok, it means not much updates during the development but there can be a few new things coming with the pack. Though only if they focus on important things like new systems or such instead of set dungeons and challenge rifts. And this patch after the Necro DLC is one of the best balance patches we have had so I'm personally pleased.
Surely I dare not to expect anything after Nev's post but we never know.
D4? Not interested. I honestly can't see it not being simplier than D3 or D2. If it's something completely new, then bring it on, if only they keep working on Diablo 3. D3 can be made a real gem with correct decisions.