I saw a blog post the other day--sadly, I've forgotten where--in which the blogger lamented that a raid could no longer "carry" one or two sub-par players anymore. Not like in Vanilla, where much of the initial content was so under-tuned that you could easily spare 5 to 10 slots in a 40-man raid.
I wonder if you could actually do this. If you could set up a system to make carrying players more viable, without lowering the difficulty of content for the better players.
Suppose you could measure a person's "PvE ability". Then, for people with a low score, you could give them a buff that increases their damage and healing output, decreases their damage taken, and maybe even makes them immune to certain mechanics if the score is low enough. The buff would scale inversely with PvE ability. Very low scores would have a more powerful buff, while better scores might have a small buff or no buff at all. Then the buffed person would have their performance dragged upwards in a raid, towards the mean. They would be less of a dead spot.
Essentially, it would be the same idea as handicapping in horse races, only with boosting the weaker individuals, rather than penalizing the stronger individuals.
Of course, the hard part would be coming up with a way of measuring one's PvE ability, without lending it to exploitation, and accounting for increases in skill and gear. It would be fairly easy to do in PvP, as you could just go off a character's personal match-maker rating or similar. In PvE, you'd probably have to conduct analysis of previous fights somehow to assign a rating.
Such a system might even help with gearing. An under-geared character would end up with the buff, until her gear caught up to the rest of the raid.
I'm not really sure if such a system would actually work. But I think it's an interesting idea.