These points have been discussed in a number of general PvP posts, but I thought they deserved their own thread:
1) The number of players required to start a match - simply put, the system is borked. The minimum required number of players on each team must be three, but the counter doesn't reset when a player drops out. This can lead to severely stacked matches (I was in a 5 vs 1 earlier). I would address this first by resetting the counter when a player leaves and secondly, by not allowing a player to join a team when there's already 1-player extra on the team.
2) Switching teams - one should not be able to switch teams. I did it earlier today, because I was the first player on my team and 4 others joined me against the sole player on the other team. Due to the faulty counting, it ended up being a 5 vs. 1 match, so I switched teams to help out. I shouldn't have to do that and I shouldn't be able to switch teams mid-match anyway! Furthermore, this leads to the possibility of being able to actually have a single-player match, which would be exploitable for raising CTF captures!