Join in progress is amazing, I'm pretty much with Kyle on this one; would rather have a random stream of scrubs than running around meleeing walls and browsing the internet on my phone waiting for a 1v8 to finish. If you want a competitive game, well hopefully there is a playlist for that for one(that doesn't have JIP, it shouldn't need it), or do customs.
Also do we really need to have the jackal discussion again? It still looks like a lizard bird.
That's another reason why I think there should be ranked playlists with visible ranks. It makes it that much more important to stay in ranked games if something like a visible rank is at stake.
I play ranked playlists for either the competitive gametype or the rank. I play social playlists when I don't feel like trying to win. That was the distinction made in Halo 3 and I think that was one of the things H3 did rate. Those matchmaking hoppers were really effective.
The thing about visual ranks is that it ties everything in. If you want to play a ranked playlist, but don't actually care about the rank, then you'll be in the lower ranks with similar minded players. It's nothing against you as a player personally, it just sorts you out. Higher ranked players have played for that rank and care about winning, so they'll be matched up together.
Drop in drop out (we should call this DIDO, there will be no white flag above my door) will be AMAZING for social playlists.
However, there needs to be a reason why people won't quit out of ranked games as well, and that's where a visual rank plays a key role.