Perhaps one of the more prevalent problems matchmade raids would facilitate is that after a while, some matches aren't going to even get to the point of failure. IME with raids or similar modes, people will stat check you or size you up as soon as the game is loaded up. If you don't have the right gear equipped, make a wrong move, or if the classes don't provide the necessary stats (i.e. everyone is a Gunslinger) it'll end before it even started. With friends or a similar method of inviting people before the game starts, you'll either know or be able to sort this out beforehand.
Some of this could be rectified by certain features, like a quick Vault at checkpoints, a system that fills in "missing" classes, and even moreso by proximity chat (which isn't suddenly going to make people who don't want to play with mics put in their mics by the way, but I digress). Nevertheless, Raids seem to be about more than just pumping the enemy with bullets like a Strike. It wont be as bad as the ones with very specific classes, but I can say it's a certainty, and one that Bungie seems to want to avoid among other things.
I like the possibility of opening it up to matchmaking as a new Raid becomes available, but don't encourage that shit from the onset. It was a big problem I had with Extinction in CoD Ghosts. Some guy would ignore all the skill challenges and people would immediately quit, which meant I had to matchmake back into another game. That's a greater waste of time to me than finding dedicated players who will communicate and strategize, whether we're more likely to win or not.
