seems like there are a few ways to look at the OS loot issue.
1. if you want tank gear, you must like to tank... so queue as a tank silly. there is not much point in OS gear if you don't want to use it so queue up and get to it.
2. Blizz should implement a UI element that toggles OS loot when you are raiding LFR. with that enabled the appropriate loot for you is drawn from both your active AND off spec.
3.Blizz should implement a UI element that toggles OS loot when you are raiding LFR. with that enabled the appropriate loot for you is drawn only from your off spec.

If you think about it options 1 and 3 are actually the same. The button to toggle which spec the loot system will use to determine the appropriate loot is the "activate" button on the talent pane. though with option 3 you don't have to play your off-spec to get gear.

I have a hard time wrapping my head around wanting to gear up a spec, but not wanting to PLAY that spec. I heal MS and sometimes OS dps. If I wanted dps gear, I would queue as DPS so that in addition to getting the gear together I would also get practice dps'ing the fights. An OS loot UI toggle might confuse people and really doesn't add anything useful to the game.