I think MM for Raids is a viable possibility BUT it needs to be a pretty advanced version of it. It needs to go farther than requiring mics. Basically steal the MMO model of queuing (and call it that so people are aware it's different):
- Start the process by entering a queue.
- That process logs your level, and your class and subclass's levels and matches you with others based on that.
- If no mic is connected, you can't enter the queue.
- Once it matches a group, the game notifies you and sends you a limited time invitation (maybe 1mn).
- Accepting the invitation locks you in to committing to the Raid and bailing on it penalizes you somehow (Not sure what. Maybe you do less damage or can't earn marks for 24 hours).
- Since this process takes a lot longer than the normal matchmaking, you are free to do whatever else until the invitation is sent.
- During the Raid, you can vote on kicking players or on abandoning the Raid without penalty.
Add in a warning screen or two explaining to the player what they're about to get in to and something like that could work, but I imagine it's not so easy to implement. There are also some flaws with it like disconnects out of your control (which happens to me a LOT), and you could plug in a mic and disconnect it later. But as an option, it's better than nothing.