Have something that involves that would be ok in my mind. But it should not be a thing for all runs and I do not think you should be rewarded extra gear or anything actually meaningful to progression.

Maby Beat a dungeon in X time and get an achievement. Beat all the released dungeons in the expansion in X time get a mount as a reward for said achievements or something. And put the requirement as Pre-Made party only else it will literally cause drama in every dungeon run, cause someone wants to watch CS's or someone is new and does not want to pull fast or they pull the wrong thing.

The way 1.0 did it, I think was more or less hated by most. It involved more or less skipping as much as possible, going in on optimal jobs only, and literally just rushing everything. If you did not do it, you literally got screwed on loot.