Introduce a server queue system, that lets you queue up to a full server.
This has multiple use cases:

• When you wanna join a friend, but the server is full l, you could just queue up and wait for the next free spot, without staring at your friend (Join button) and running into a potential "server is full" error.
• When you are in a full squad, the game hides every server that has no capacity for your squad. Most of the time thats all servers except of 1 or 2 that are basically empty. Queueing up to a fuller server would be a nice feature.
• When a server closes, you could drop the entire population on a new server, if necessary queueing up people who are not fitting anymore.