The more I think about this idea, I just think who ever is going to deal with the headache of making the arrangements should just do it for where ever. Even if it is Mammoth. It's not like people have to go. If they want to do this thing, they'll figure it out.
Getting a block of rooms at a discount is less committing than renting a huge house. That puts it back on the individual not the organizer to some degree. You'll just have to have a cut off date to reserve by and such.
There is just no way people are going to agree on a spot in the West. Unlike the East Coast, it's a dime a dozen for world class spots. Every Western state has awesome riding.
Just my thoughts.