Now and then I've advocated for adding a 6th person to the standard group. This would free up more space for DPS. But then a gnome got me thinking. No, not about trajectories and "can I punt her past that?" Instead, about those rare-these-days sub-5 groups in which people actually try and struggle and fight and play. They know there are better ways to get rewards, so it's all about the experience, and I don't mean the experience that makes our characters ding, but perhaps that makes us players ding, as we level up our patience and tactics. I've run into this myself, and also enjoyed it.
Maybe this can become normal.
What if Blizzard dropped groups down to 4 people? It would hurt the DPS, but let's remember: DPS hate us, by us I mean tanks and healers. Why else would they play the way they do? Never attribute to incompetence that which can be adequately explained by malice. But that's beside the point.
With one less DPS, even with the tank being one of those who matches the DPS, that's still a 25% loss overall. That's going to make it trickier to just AoE everything down or burn through mechanics such as needing to kite or switch targets or whatever else. We'd each have to play a bit smarter.
It would be slower. Is that really so bad? I hate to think that we've all being running miserable randoms just for emblems. Would it be an improvement to run them slower but actually enjoy them?
Instances would still be tuned for bad 5-man groups, so the change wouldn't just be "one less person, easier instance".