I enjoy this event.
For the two maps that I joined I picked a time that I was going to join, and invited a lot of people that I know to all join my team. So for each one we ended up with a robust blue team of around 15 people that I have played with before, and of course the random players that joined. It was a great experience in cooperation and communication.
I do need to remember to line up some competition for the red team next time to make it more interesting. All of you people who want to do an alliance vs alliance battle on a 100 player map this event is for you.
As always every event may not suit every player, but with a bit of planning ahead this event is great for a group of people to play together on a larger scale than is normally possible.
For the next time this comes around, would it be possible to put a level 1 airbase in every city? This certainly isn't enough in some places until planes get researched to a higher level, but it will improve the access across our teammates land. Certainly it would be ideal to have active teammates who follow directions, but that is harder to guarantee 
As an alternative or perhaps an additional suggestion, having research unlocked through day 16 would allow longer ranges of planes, and access to higher speed units which are key when you have to defend an empire spanning an entire continent, or assist your allies on the other side of the world. Typically in a 100 player map it is day 16 to 24 when you start venturing to the far ends of the world, and you have high speed units, aircraft carriers that are capable of carrying Tactical bombers (day 24) and a well developed economy.
The other side of the coin here is that planes are largely useless in this event game. We are seeing various combinations of tanks and infantry units on a large scale, which is interesting. One of my games I am finally about to attack a target with my planes for the first time here on day 9, yet the game will be over by day 15 in my estimation. That means I was rather foolish to build planes and spend the time and resources getting airbases across the continent, just in time to watch my allies break through from the other side.
So if we skip the airbases in every city idea and simply unlock research to day 8, that will enable more variety on the battlefield. Tank destroyers, Medium tanks, Railroad guns, and Motorized infantry would be interesting to play with in a plane-free environment.
Another suggestion that might be worth discussing is country choice. I don't know how to solve the issue of the game starting when full if the last few people don't want the remaining few countries, but if that technical hurdle could be overcome I think that this would lead to fewer players who join, get a random country that they don't like, don't want, are scared of their neighbors, or aren't near their friends, and immediately archive the game never to log in again. Since there is no limit on joining any number of games (within reason of course, there is a hard limit of 50 games that anyone can be part of at any one time) there are players who will join several until they get a country that they like. This leads to a less fun experience for the active players when there is a high level of inactivity. (this suggestion also applies to the 73 player "all in" historical event)