The biggest problem with GIFs would be the colorspace: GIFs are usually limited to 256 colors. Color quantization from a JPEG to GIF would kill the photo.
The whole "living image" sounds nice. If it was possible to create a format, say "AJPEG", out of it, it would be awesome.
Great, I'm not actually sure how the iPhone photo library handles GIFs.. but I'd much rather be able to choose 'export as GIF' & 'export this frame' than to save all 100 photos.
The Camera Roll will apparently host them, but not show them as animated.
Unless you roll your own viewer, many devs suggest using an embedded UIWebView to animate it.
Otherwise it kinda gets treated as pass-through for most of iOS. The Messages app apparently animates them nicely, and for some is a real motivation to include the feature. (So they can send animated GIFs to their friends.)
Could you take the 'trimmed' section and create a looping GIF from that? (Can I do that already?)