This console generations has another 2-4 years to it, don't worry (most consoles have a 'runtime' of about 6-10 years, if you examine the trends)
I havn't heard of a NextBox and the PS3 is just hitting it's stride. Also the 360 is in no way completly taxed, folks have said the same thing about EVERY console. Whats at it's limit is what you can do with pure, brute processing power. About now is when the BEST games come out, when developers look for elegant solutions to problems instead of MOAR PROCESSING! I will point to games like Shadow of the Collossus, Okami, and the many great 'late life' SNES and Genesis titles.
Think of it as a maturation process- the shiny new glisten on all the consoles is worn-off. We've moved out of the annoying 'teenager' stage of the current-gen; no more abysmal Launch Titles whose only saving grace is pretty graphics, we've become jaded and used to the 'nextgen'. Now more refined products can, and will be made.
Just relax, you've got a couple of good years left in your console, whatever one you purchased. Xbox360 is entering the "Middle Aged" Phase the PS2 did, wherein it recieves the most developer attention and tends to get the most mediocre to good games (along with plenty of aweful ones); the PS3 is warming up and finally getting the attention and titles it needs to be strong; and the Wii/Nintendo has finally caught on steam and is hitting a strong stride.
