Duh.

PPC emulation can be done, check out http://www.dolphin-emulator.com/ but emulating another architecture means a significant drop in performance.  The powerPC is a great chip, way better floating point than AMD/Intel but it is not used often enough.  IBM announced a big initiative to try and revive it's fortunes in big data settings with the power 8.  But unless you can recompile and port... it is not useful.  Great for linux folks, hell for windows end users.

The specs on PS4/XB1 are not sufficcient to make emmulation practical.

As for the OP, I take it as a given that even at 600-1000 range a steambox will be significantly more powerful than any console this gen.  I don't know whether I will build my own or buy thiers, but unless it is a hasswell iris pro with no dedicated card, it will do just fine spec wise.  The haswell iris pro will still do 1080p  at 60 FPS on some games.  The AMD apu designs are what you are getting in the consoles.  even an AMD A10-6800 will be similar to the performance of this gen of consoles. That would mean a very cheap steambox.

I want an NVIDIA 760 or 770 for a steambox, at 1080p livingroom resolutions it would kick ass.

Consider me a day one steambox owner either way (build or buy).  Digital distribution, modding, kerbal space program... I'm in.

^This!  They might make three levels, and Gabe has reportedly said you can install Windows on it.  So we can assume the high end will be a good PC build.

Rumer has it there will be three levels.  And I think the lowest one will be a low priced one for the people that just want some steam games to their TV without maknig a fancy PC with a sub $500 price.  Sure they might have another box to make it easy to stream from your PC for thoses with a fancy PC.

I am mostly curious to see what they do with controllers.  I think it will either be a tiny niche market, or a huge hit.

VLIW5 is AMDs older GPU architecture which, based on some pictures of the WiiU insides is likely what the GPU in WiiU is based on. The "High Definition GPU" is marketing talk as most mobile phone chips sport "High Definition GPUs". 

He's probably right about the emulation. The CPUs in all three next gen consoles are all fairly weak and relatively easy to emulate in raw power terms. The core architecture is supposedly the same for WiiU (from Wii) so even with its multi-core nature, it'd be relatively simple to do. The GPUs and emulating the specific drivers for each console's GPU is more problematic. As he said, bandwidth would also be an issue and generally, the hardware you're running an emulator on needs to be significantly more powerful compared to the device you're emulating. Therefore, WiiU as the weakest of the 3 would be the easiest to emulate.

I don't think anyone would bother though.

Who would buy the Steambox? The audience for it is just not there.

this could russle some jimmies.

All of this is wrong.

Really detailed and informative post there

Is this discussion now about emulation? And well, many posters don't know much but feel entitled to say something anyways. As a programmer I know something, but that something is enough that I know I can't decide if WiiU or PS4/XBO are easier to emulate. That said, it's not the difficulty alone that makes emulators possible or impossible, it is also the will of the community to do it. As many PS3/X360-games are also available on PC, I assume it will be similar with PS4/XBO. Nintendo on the other hand makes interesting games that don't come to PC, so the interest to build an emulator for Nintendo-platforms is much higher. That - and not technical reasons - will lead to an emulator of WiiU faster than for PS4/XBO.

Now to some technical stuff:
1. Many here are focusing on CPU. While it is right that CPU is part of the emulation, you aren't near a functioning emulator with CPU alone. There are many chips and architectural stuff, that needs to be emulated. So don't focus on CPU alone.
2. That said: while it is difficult to emulate the catastrophic x86/x64-design (that has backwards-compatibility to eons before), it isn't needed to do so, if your emulator runs on x86 (PC). Modern x86-CPUs allow to run code in an virtualized environment, so an emulator can use that. That's the case for PS4/XBO. So CPU-emulation you can see as basically solved without much loss of performance, but as I said in 1, that's not even near a full solution.
3. Architecture is VERY different on consoles. As an example I name unified memory on PS4 - that will be a burden to emulate. But all three have architectural details that will make emulation a hell.
4. What allenmaher says about emulating PowerPC-architecture is true: emulating that will be a big loss of performance. But that is true of all CPU-architectures. As I said in 2., that will not be so hard for PS4/XBO. BUT, that is not the only chip that is needed to emulation. As GPUs are very important for modern consoles, they will be the major technical difficulty in emulation. They execute code like CPUs, so it is not simply a matter of putting images to the display. I don't know if Nvidia and AMD have similar tech for running programs in virtualized environment, like x86-CPUs, but if they have I doubt it is very common with consumer-graphic-cards. So this part will mean a big loss of performance, expect some years before PC can emulate any of the three. Probably at the end of the gen.

To be onest, this is like Half Life 3, no one really knows whats goinig on with it, it's all just speculation so far.
Anyway I'm expecting it to be more powerfull than Ps4 by a good margin, and to cost from 500 to 600$.