I think the Xbox720 is going to have similar Specs like these:
CPU: ATI Radeon HD6670 1GB GDDR5 90$
GPU: AMD Phenom II X6 1090T 6x3.2GHz 148$
RAM: 2GB DDR3 1.333GHz 26$
Custom Motherboard: Company Unknown ?$
Dual-Layer or Blu-Ray Drive: 30-50$
It would be around a 300-400$ Console again and these parts are Available now and specially since Mircosoft is working on the Xbox720 since early this Year. So by the time the Console will be released these parts are going to be cheaper and more Profitable for Mircosoft. Not to mention they said the Next Xbox will have an AMD Processor and an ATI Graphic's Card again, which i put on my list.
With these Specs the Console would totally be ready for Next-Gen maybe not totally overboard like a PC but Consoles where never known to be like that and anyway with these Specs it won't eat as much Power either. Making it a Idle Next-Gen Console.