I don't see Destiny as being about stacking 100, or 50, or even 25 people (visible to you) in a single area. I think they're more shooting for a feeling of adventure and danger you get from being alone with your fire team combined with the idea that other teams are out there and you'll occasionally cross paths.

For public events I'd think the number of people would be capped around 20 given that multiplayer in Halo could go up to 16. But then, we've seen one public event. What if it was a tiny one, and big ones involve vehicle battles, and tons of enemies. Maybe the player count can go a lot higher than I expect.

It would also not be surprising at all if competitive allowed a considerable amount of extra players than cooperative.

I don't see Destiny as being about stacking 100, or 50, or even 25 people (visible to you) in a single area. I think they're more shooting for a feeling of adventure and danger you get from being alone with your fire team combined with the idea that other teams are out there and you'll occasionally cross paths.

^ This.

My interpretation is very much along these lines. Right now in Halo, there may be several thousand people in a particular Matchmaking hopper but only 8-16 people are ever playing the same game. I imagine Destiny will do similar matchmaking; as long as you're in the same physical location, you have a chance to be matched with some small subset of the population. Quality of connection and preferred style of play may be elements that are taken into account, and we'll always be matched with our fireteam.

Has anything been said about difficulty scaling for solo versus fireteam, or difficulty settings at all? I'm really curious how difficulty settings are going to work, and how that will work out in public events. Will the difficulty be somehow automatically scaled to our skill level, or will we have instances were the difficulty could be too easy for one person in my fireteam and too difficult for another? Can I set my own difficulty level and play alongside friends that are playing at another level? Can I replay missions on different difficulties?

I don't think I've heard anything about difficulty scaling. That's a really great question though. I've always played Halo on Heroic/Legendary, but my sister would hate to be stuck playing that with me. I wonder how they'll scale that in Destiny...

I honestly don't know how different difficulty modes in the same game would work. I guess they could just alter the damage tables for each person, but whether true or not, I've always imagined that difficulty levels were more sophisticated than just having different damage tables.

I've always been interested in dynamic difficulty scaling. (I'm not a big Call of Duty fan, but I'm intrigued by the Squads mode they just announced.) I know the idea has been around for a while, but I don't think I've ever played a game that had it. I imagine it might be problematic or it would have caught on by now. If Destiny had something like that, I'd still want static levels. Sometimes I like to explore on easier settings; other times I like a real challenge.

We trimmed a whole bunch of questions from our Chris Butcher E3 interview - mostly because the answers were "we're not talking about that right now" - but we'd asked this question, and his answer was

So we're not really getting into the technical details around that, but generally speaking, the way it works is that no matter what your character's power is, and no matter what activity you're on, we make sure it's always a satisfying shooting experience. Now, obviously, there are experiences that are more difficult than others, but it's never unsatisfying. You never trivially just make the content ridiculously easy.

That's a pretty good non-answer as far as non-answers go. Chris's comment suggests that a lot of thought went into this problem and I trust that they've figured this issue out (because that's what they do!). Still curious about how it works, though!