Neat ideas, and, as fun as it would be to be able to pop into Combined Arms at any time to do up those vehicle kills bounties (Bungie fix this please (oh they're fixing it in TTK good thank god)) it wouldn't work. They have many playlist types and if all the options were available at all times (even without factoring in extra modifiers like 'Inferno') it would be two things: 1, the lesser, it would be daunting to the newcomers Bungie is trying so hard to get to play Destiny, to click that little Crucible button and see over a dozen and a half options to choose from, with only a little info about each. 2, the more important, the more options the players have at any given time, the longer you'll have to wait for however many people you need to play with, sure in Control the time to wait might not change all that much, but if you wanted to jump into a game of Inferno Doubles or something just as vague, you could be waiting awhile. The best I could see happening for this is a compromise. Instead of 'all' playable options, we could have 'more'. And even some system beyond checking-the-Internet-to-see-when-salvage-will-be-back-up, so we could know when our favourite game type will be back, and see it in game. Maybe if we had maybe two extra options where we usually see Combined Arms type instead of just whatever's there at the time and (sometimes nothing even), it would be better I think. Maybe always have one type of Inferno running, and adding maybe one more game type to the consistent 4 (Elimination?), and a more consistent HoW playlist (because I want to play the HoW maps but I don't like inferno xD) and always have something in the section in between and below Clash and Rumble, maybe that would work better. As for your idea about Private matches not messing with K/D (I presume for things like gun testing and whatnot), I think it's a interesting idea, and something they should totally look at implementing, but I have no idea how they'd do that, because have a mode that is just cut out of K/D seems like a weird fit. Maybe a way to turn on PvP for gun testing in patrol with a fireteam to test there? I don't know, but it's definitely something to look at. Great ideas!

I think the private lobbies not impacting global stats would be so you can't boost your friends. At least that's how I saw it in my head.

Actually that's a really good point, though I think they're should be some sort of option for that, because friends would still like to actually play for real with their friends too I'm sure, still not sure how they'd implement things like that tho

You could still have a ranking amongst your friends. That would make it competitive.