A tweet by Frank Shaw, lead communications for Microsoft, seems to confirm that the system requirements for Windows 10 will be the same as for Windows 8.x.
You can view his tweet here, where Shaw was giving the WSJ a hard time about their post that says not to buy a new Windows 8 machine and to wait for Windows 10. Obviously, this is counter-productive to Microsoft's message and Shaw was chiming in to say that this advice was foolish. More so, he stated that the hardware requirements would be the same, so buying a Windows 8 machine now will not impact your ability to run Windows 10.
As a quick refresher, Windows 8.1 specs are listed below:
Processor: 1 gigahertz (GHz) or faster with support for PAE, NX, and SSE2
RAM: 1 gigabyte (GB) (32-bit) or 2 GB (64-bit)
Hard disk space: 16 GB (32-bit) or 20 GB (64-bit)
Graphics card: Microsoft DirectX 9 graphics device with WDDM driver