I was just watching my old guilds 10 man Algalon kill video from back in the day and was getting all nostalgic.
I would personally love to see another Ulduar style raid, where you engage the hard mode by performing some sort of specific action. For me Ulduar was the greatest raid since TBC and gave both the normal and heroic raiders something to do without having a toggle switch. Another great aspect of the instance was the unlocking of Algalon, which was a really unique and awesome encounter (I don't think we've seen a prettier boss encounter).
I know that blizzard loves their current normal/heroic raid model and probably aren't going to change things. However I would really love to see the reintroduction of Ulduar style hard modes at the expense of the heroic check box.
What do you think?
Video for anyone interested: http://www.youtube.com/watch?v=xok5VRMCVH4