IMO, the iMac Touch will be released either with or shortly after Lion.
Let me explain why I think the iMac Touch could easily be reality :
1) The technology exists. Dell will be selling a 21.5" IPS Multi touch screen in the coming months. It will probably be fitted with LED backlight too, just like the 21.5 current iMac.
2) Lion will clearly be built with multi touch in mind (first bullet point of the unveiling of Lion). What we saw at the preview is only the tip of the iceberg IMO and it already showed that you will be able to do a lot of thing only with multi touch gestures.
3) As said before, Steve Jobs only said that multi touch is dumb when the screen is vertically oriented. With the patent showing how an iMac could transform in a computer with horizontal screen, I think this problem is taken care of.
4) I can already see the reveal showing the crappy Acer and HP, with Jobs explaining that it wasn't done right : slow computer, OS which isn't built with multi touch in mind, poor screen, multi touch that suck, etc...
5) The whole "Back to the Mac" clearly apply to the hardware as we've seen with the MacBook Air. What's a better way to express that philosophy than a full fledged desktop Mac with a multi touch screen ?
As for the specs of the next iMac line, I think (as always

) Hellhammer is pretty spot on.
We know the CPU in the top of the line will be great, that's why I'm much more interested in :
1) What's the deal with the Mobility Radeon 69XX performance ?
2) Will Apple finally ditch the Super Drive ?
3) Will Apple put some kind of MBA-like SSD ?
4) Will Apple put light peak and or USB3 which would make the iMac more future proof and much more extendable ?
I really think that the 2011 iMac (the 27" of course) has the potential to be a killer computer if Apple does the right choices !
