Hi there,
I'm working on a All vs All mode for multiplayer, so you can see who really is the best one
This post is to explain the kind of stuff I have to go through when I get a feature request like this and people wonder why it's taking a long time to be implemented. Usually when you develop stuff, things that seem to be pretty simple to others, are actually a pain in the butt to implement. This is what i'm going through right now:
1) In All vs All, which team do you play?
Since there is no team, I have to allow to be in any plane. This gives me two choices:
a) Allow the player to select his/her team and plane upon entering. But this requires a new screen, with new design, more $ to get it done and wait and see.
b) Allow the server to randomly assign the player one. It's easier but also takes time and tests on the server for this. I'm going this route while I wait for a new screen.
2) Friendly kills and points?
I have to change the server so that it detects when you are on All vs All mode and disable friendly kills. Otherwise you get banned.
3) Friends and Enemies?
The game gives you red or blue depending on which side you are on. In this case I have to add a whole new bunch of code to detect you are on All vs All so that all look like enemies: red dots, arrows, independent of what airplane they are using. Lot of work on the client side :/
4) Game ends... when?
There is nothing to bomb or capture. What's the objective? I'm thinking first to hit 20 kills wins. This requires changes on the client to send proper notifications and also on the server to detect the game is over.
5) You begin the game... where?
There are only 2 airports, meaning, if you respawn and 5 seconds later someone else respawn, he/she would nail you down non-stop. But you can't have airports all over and the location is important so what I did was use the carriers. You will randomly popup at either the airports or the carriers.
6) Detect the mode.
The server has to know you are All vs All and do not allow you to 'capture the carrier'. The client has to not only detect that everybody is an enemy but also remove the hangars bombing, disable the capture the carrier and reload on any airport/carrier in the game.
7) Time out.
Just in case the game goes on for 2 hours, I have to kill it at some point otherwise people will just be coming back to the same game type which they may not like.

Detect whether the change is out on android or apple.
Since updates don't show up at the same time (i always have to wait for Apple to approve theirs), I have to detect which device you are using on the server side and act upon it. Not all players will be able to play All vs All until it's out for all.
9) Test, test, test... without disrupting current players.
I've never released (and I don't know anybody who has) a major update without bugs. So I usually have to release them on stages and beta test with some players. Then listen to the input and change it accordingly before an official release.
10) Sleep. More. Often.