Yes, the count of people is at least 40 and growing. Most of us have homes that can fit them all in, the ones who are willing to host definitely have enough room. But yes, MILs home is the largest and she really did do a lot to the home to make it entertainment central - so I understand some of the reluctance that can come with switching.
Not every set comes every year due to traveling to their other extended family and that has become a source of tension, they will host 2, 3, or 4 parties for one holiday and pressure everyone to come to each in order for everyone to spend time together at some point. Every holiday though, it is stated again to set the date earlier, at least give 2 weeks notice and we realize that all could have made it. It's just not happening currently, MIL & the 2 sets wait until a few days before the week of the 25th in December and start scrambling and well, crying & whining. But in hindsight we are all able to pinpoint days that we all could come without needing to do multiple events in order to make it happen. It's really coming down to lack of planning & organization AND unwillingness to change to accomodate current reality.
It's very important to MIL, but so are the other traditions and it has become really out there due to the two sets wanting everything to be the same in order to please her, and well themselves in the process. It's very lopsided at this point, so it makes sense to DH & I that there becomes some sort of equalizer. We can't for sure pinpoint what is most important to MIL & the two other sets because they will say everything is important and have become unwilling to part with anything in the past, yet now it's too obvious it is not working and too many of the sets want change.
So the solution to rotate hosting would solve most of this, imo - they get to keep other parts that are important, the gift exchange, the food (most of the would be hosts agree they would host meals similarly wherein people could bring food if they want, just a slight change in that they are not handing out to the sets of what they ARE making, just the offer to bring what is most important as far as food to them). The changes would be location and organizational details, which imo, is not much considering the situation - although I understand they think it will be.
And yes, definitely DH will do the talking (he is reading here too) and I'm just there to support him but will probably chime in here & there. I understand that this is a sensitive issue to them & others, but it is also important to us to feel a part of the holidays and currently it is just not happening.