I sent in a new suggestion to Blizz, new to me at least, and I'm hoping it actually goes lives some day. It's probably been suggested already, but hell, couldn't hurt to mention it.
Dungeon/raid difficulty option: Gear scaled. This setting would be intended for "old" content. Currently I would qualify this as upto and including Cataclysm content.
The intent is to allow level 90s, for example, to do a dungeon/raid run with other lower level players and retain the bulk of the difficulty/challenge that these adventures provided at the appropriate level/gear ranges. No, it wouldnt be perfect, but the design could/should be near enough to be usable and enjoyable.
Not everyone wants to plow thru old content constantly do they? Guild "fun run" nights could be sooo much more interesting this way. i welcome your thoughts on this idea.
Also, what things have you guys suggested to Blizzard? Other than to stop drinking the kool-aid or nerfing your favorite class... (lol)