Well yeah, of course there will be RTS games as good as C&C and Starcraft. There have already been better ones.
Technology moves on. In the same way that Doom was revolutionary, as was Half-Life, as was Half-Life 2, as was Crysis (well, not really, it was just pretty and I needed a third game), older RTSes just don't stand up as well compared to newer ones that learned their lessons. (probably explains why people seem to hate Half-Life 2 now- when it was released, it was pretty, compelling and had physics- which are pretty old hat these days. Except for compelling. I can still count the number of videogame females that I don't want to stab with a rusty implement on one hand. Alyx of HL2 is one of them.)
I've had more fun with SupCom than with C&C, and I've had more fun with just about any RTS than Starcraft.