"No matter what way I cut it, I can't see a way for more than one player to operate a Mech without drastically slowing down the game or creating inter-player conflict."
I don't think it will be too bad. Slowing down the game to increase inter-player interaction is worth it in my book, and I bet they'd agree on tactics quickly a lot more often than not. Plus, if you don't need all the people of the party in the mech, the players who work together best are probably more likely to be riding together. I'll update this after my playtest (which will likely have 1 2 person mech) to share how that goes though.
