So people want fireteams, but I think the implementation is not so simple. You have to consider how they will communicate.
Some people want an extra fireteam chat button. Do we want more complexity? I do not think so. Some will say, "it's only one more button", but it isn't the button that is the issue. It is the principle of keeping this game simple and easy to use.
On the principle of being simple and easy, some people rather just have one big squad that moves as one. A lot of firepower controlled by one leader.
Besides, where exactly are we supposed to find two fireteam leaders? It isn't like every player in this game is a team leader. A lot of times, we have a lack of team leaders just for squads.
So let's do this: have squads have the option to be turned into a fireteam-able squad. A button changes the color of the squad name or an icon shows up, and the squad leader now has fireteam capability.
You can see which squad you can join in which you have the chance to be a fireteam leader! Or one you want to avoid because you don't want to be assigned as a leader.
How about fireteam comms?
Well, make it so that the "squad chat" is now your own fireteam chat. When a fireteam member uses his squad chat, it is actually to his fireteam. When the fireteam leader uses his squad leader chat, it is actually chat between the SL and two fireteam leaders.
For the SL, his squad chat only goes to the fireteam leaders while his squad leader chat remains the same.
"But I need to be able to talk to all my squad members!"
Then use your local chat.
If you want fireteams, that means having two leaders to lead them for you. It is leading through delegation. This is how platoon leaders lead. If you do not like this, you have the option to stay as a normal squad.
What makes a fireteam isn't weapons or equipment. What makes a fireteam is how you organize and communicate.