I laugh at the "purists". You're the type that resisted computers (I'm doing fine on my IBM, thank you!), resisted Photoshop, resisted digital cameras, and in the end, you're shooting with a K20D, tweaking your RAWs with Lightroom/Aperture on your Mac, and, yeah, why not, use Photoshop now and again.
It will be the same for this "video thing", and 10 years from now, you will all be shooting a cam that does video, and importantly, you'll be loving it. You can quote me on that. 10 years from now. You really can, because I've been RawheaD on the 'net since 1995, so I'll be RawheaD on the 'net in 2020 :-)
The debate about whether or not video on DSLR will replace dedicated video cams (and/or vice versa) is besides the point. The point is, if you're not bound by technological limits, the possibility is there so that you can, e.g., depress the shutter, and it will record 4K HD video for the duration @ 120fps, and if you so choose, can select the best frame as your shot.
Some pompous commenter up there somewhere suggested this mode of photography as being blasphemous. I laugh. You've never used a motor drive with your film cams back in the day? You've never shot "continuous" or even "burst" mode on your Pentax? You can ridicule this idea if you answered no to all those questions, and will continue not to. If you have, then WTF? It's the same principle.
I'm not suggesting *all* shots should be taken like that, and I don't need lectures on the art of "capturing the moment." I also shoot 120 film, thank you very much. The question I posed was "Who wouldn't want such a capability in your cam". Now, if you only do landscape photography or highly controlled studio photography, maybe your answer is "Not I". But, if you're honest, and you do sports photography, bird or any kind of animal photography, anything with movement, really, then you are going to want it, and if the capability is there, you are going to use it. Hell, even in the studio, fashion photographers would definitely use it, like that Vogue cover (or whatever it was) that was shot with a RED cam.
Similarly, on the video camera side (RED is a great example), there have always been lame "still" shot capabilities, lame because the sensor size was always lame. But, when you get high quality video, like RED, you suddenly have the capability to extract a high quality still from video, and you can bet you'll see more and more such stills. E.g., movie posters where the still image is a direct extract from the motion picture that was shot using 4K HD. And a lot of those shots are gonna be better looking "stills" than what many of you could ever shoot
(yeah, that includes me).
So, go ahead, be that last guy that switches over, like those last of the breed film photographers that are now, finally, moving over to digital (btw, I have a lot to thank those guys; I recently made several sweet, sweet MF lens acquisition from such folk). In the mean time, the world will move on, and unless you are among the cream of the crop photographers, it will have left you way, way behind.