With the average PC using maybe an 80+ bronze rated power supply of 450 watts or more, the actual difference at the wall when its idling at under 10% PSU load may be a lot less than the numbers suggest.
By comparison an 80+ gold PSU is a lot cheaper than a motherboard and CPU and will reduce power consumption by a similar amount.
It’s not an either or situation if you are building a new system. If you want the lowest power consumption then you address each of the components.
The most impressive results should be the desktop BGA chips with the Iris Pro graphics as you get good integrated graphics performance for its class along with all the other benefits. Not sure if Asus or others will release boards with those soldered on and then there’s the issue of heat-sink mounting due to the die being bare; would make a lot of sense in an ITX system.
The CPUs are very expensive in the UK right now even for a new launch; should drop hopefully.
As for the power consumption it is clearly lower than Ivy Bridge and compared to an AMD system in the same class even more so as the 8 core platform requires a discrete GPU; Trinity is a different class of chip.
If you are talking about an upgrade it clearly is either or.
Also as Ivy Bridge goes EOL and prices drop to clear the channel, there may be a good value proposition to stick with Ivy for a new build so there is a choice to make.
There will be no desktop bga chips unless you count the NUC and similar boxes but those will be limited by their notebook-like tdps.
I'm glad to hear the 23.976 hz issue was fixed, now Intel can make a decent htpc without adding discrete graphics but they need to release an i3-4225 or something to compete on price with Trinity/Richland.
Lastly, there are going to be a lot of people with a not quite Haswell compatible 80+ or Bronze power supply who work around that by disabling most of the new sleep states and there is no way a computer like that will consume less power than an Ivy with a Gold or Platinum rated PSU.
Haswell is good for "ultra books" and maybe 24-7 servers who idle almost all the time.