and as i mentioned in another post about 2011 iMac's , don't ditch the chin
make it removable with 3 screws to access two s-ata slots for HDD's like on the xserve , and one full size PCIe slot for a GPU of choice
basic iMac then comes with a 128gb ssd which can sit somewhere behind the display and has a geforce 320m somewhere on the logicboard
that way you can have a real basic iMac that can be upgraded to meet personal needs with a top of the range GPU if you need one and with a couple TB hdd space if you need it without cluttering up the desk ..which actually was the main reason for a all in one computer
and ideal alongside the 21.5 "and 27" again a 17" or 18.5" model but with all the internals of the MacBook Air plus one slot for a HDD that could be on sale for £799 to cater for people who do not need a big screen but one thats bigger then a iPad or a MacBook has to offer , who dont need a i3 ,i5,i7 processor and because of the MBA internals this iMac could be as thin as a MBA or just as thick to give space for a 2.5 " hdd