Power for my rear speakers isn't an issue since I have 4, if not 6, sockets on my back wall and only 1 is being used. Is your friend using wireless speakers or does he have a kit that sends the wireless signal over to them? I was reading up on the Rocketfish kit and the main issues I see are:

1) CD Quality Audio - Sure CD Quality is good but I'm going for a Dolby Digital HD / DTS HD setup here so it would be nice not to lose that quality on the rears.
2) Sound Lag - Potentially a huge issue but I'm fairly certain it could be counter balanced through receiver settings - ie. set the rears at 0.0m away and over compensate on the distance of the wired speakers to make up for their lack of this lag.
3) Powering on and off - I don't want these suckers running 24/7 when I use them 2/... a couple times a week lets say and it looks like both the sender and receiver have to be turned on/off independently AND the switch is fairly awkwardly located. Digging behind the component shelf, and potentially behind my couch, each time I want surround makes it sound like more of a hassle than routing wires through the wall in the first place.

Anyways, as for the setup you're planning, it looks good but I personally wouldn't want speakers embedded in my walls. The mid's and low's produced by surround speakers come just as much from the housing as they do from the actual speakers themselves. In fact, I don't even like having my bookshelf speakers closer than 1-foot away from a wall because that can also interfere with their sound.