Actually, hardware wise we are already at a good point to emulate consoles like the Wii U/Xbox360/PS3. An Intel Skylake architecture CPU due to release this year, is going to be more than enough. While the Xbox and the PS3 have high frequency CPUs, their IPC is abysmall compared to modern x86 cpus.
The Wii U cpu has almost the same cpu as the Wii, just 3 cores instead of one and double the speed. The 3 cores are not a problem, since we have unused cores on our systems anyway... The double speed is more of a concern, but i believe a modern cpu will do fine...
The problem is reverse engineering their apis and architecture and emulating it. This will take MANY years of commited effort from skilled developers... Modern consoles are fairly complex. It is not like earlier 8/16 bit systems where even one individual could create an emulator by himself...
So, the problem is not one of hardware, but of software. It will be really hard to find people willing to commit the effort for such a task...
PS: One other reason we don't have Xbox360 and PS3 emulators is because there is no interest in getting one. Most games have released PC ports, and those few exclusives are irrelevant and not worth the huge effort. Same with the original Xbox, why emulate it?