I like this idea, it will allow for alternates to switch in in an Operation in case people have to pull out. Thereby to further it I would suggest allowing an observer queue (like you mentioned) and an alternatives queue. You could queue for both, this would allow any alternates (i.e. if you have a raid group of 8 but 10 ppl want to play) to continue with dailies until a spot is vacated (say certain ppl can only do the 1st 2 bosses)
I like that, allows people who only want the weekly to get their coms while letting the group finish the Op with alts.
I'm unsure about the coms myself, wanted to give the observers something since they would invest the same time as the raiders who get gear and coms/creds. Maybe social pts are enough, or there could be a daily/weekly for obs who knows, not attached to that part really.