Just an honest question, but do you like the glossy screens? I personally get quite annoyed by them at times, and find matte screens to be a more relaxing (/dull) experience. The glossiness does however make the iMacs look good in stores. The colors a bit more vivid, and they also tend to show mostly whtie/bright footage on them which hides the mirroring effect.
If one has to use their laptop/desktop out in the sun (and in a fixed position), or under non controlled light, then a non-glossy is probably the better option.
Personally I love glossy screens. They get glare sometimes, under direct light, but nothing that an angle change can't fix. Besides I don't want to be using a laptop under direct light anyways -- and for a desktop which is used inside, that's a non issue.
Non glossy screens (which I started with), I now find smudgy and hazy, and with much worse (gray-ish) blacks.
I had a lot of issues with one in an office that had tons of windows, some times of the day it was super hard to see. But the colors did look pretty good.
I'm partial toward matte too, just got an Asus 4K display that's seriously impressive, never expected them to brand really nice displays.
I really like the fact that they used 4096x2304 instead of 3840x2160 as the screen resolution for the 21.5" retina iMac.
Let's hope this new resolution catches on quickly.
I agree that it's useful for a TV but the 21.5" iMac is too small for that anyway - however if you want to edit 4k video, it's super useful to have extra pixels to be able to display a full UHD image with some GUI elements surrounding it.
They've used the DCI 4K resolution standard as the basis for their 4k screen, which is defined as 4096 x 2160 at 16:9 aspect ratio. This screen has a 16:10 aspect ratio, thus 4096/16*9 = 2304, the vertical resolution on the 4K iMac.