From my experience, the quality of the SlingPlayer iPhone app over wifi is already pretty poor at standard definition.
I've taken to using a UK-specific live TV streaming service (tvcatchup.com) as their picture is so much better than the one I get streamed from my SlingPlayer Solo on the same wifi network as me! 🙄
So in summary, I wouldn't hold out much hope!
From what I understand the Slingbox Solo, and Slingplayer stream on some sort of WMV standard, which is why the quality is never the best, even on slingplayer for mac, (And why slingplayer is such a resource hog on the iPhone, their application essentially has to software decode the WMV stream rather than use the native h.264 support). (The Slingbox PRO also is on the WMV standard but I think it also has support for an H.264 MP4 based stream, though slingplayer for iPhone is still built around the WMV stream) this is all my very limited understanding of the whole situation so I could be completely wrong.
This is the thing I don't understand though, if you use their newer slingplayer plugin for web browsers (
http://watch.slingbox.com/watch/sling_player ) it actually looks better, and runs better, than slingplayer for mac or iPhone. If they can do this in a browser plugin then they have to be able to get this kind of quality on the iPhone 4 (And iPad) over Wi-Fi, ugh it just frustrates me how slow they are at updating a $30 app, (The new android version seems to have much needed improvements to the interface as well, I hope those are coming to the iPhone). If they would just fix some usability issues with the controls, and refined the video quality this application would be a major killer app, instead of being just kinda half-baked as it is now.
Taking my TV with me wherever I go is one of the few dreams I had about the future as a kid (Seriously when I was 7 I considered buying a giant roll of coaxial cable and stringing it out the car so that I could get TV wherever I was, obviously this plan was flawed, but I was 7). Now that we have video calling, internet wherever we are, and 3D TV's and Cinemas, most of my childhood dreams about future technology have come true, we are so close to the future I can almost taste it.