Every strategy I go down seems to arrive at a dead end. Predetermined is inflexible, best of x doesn't feel like traditional Pokémon. The not knowing what the other person will choose seems ideal, but that wouldn't work in thread. It might work if I were to choose a Pokémon before you posted and go with it no matter what, but it doesn't work for PC battles. One person will always post after the other, and the only way to keep them from choosing another Pokémon is the honor system. The only way I can see that working is if both players message me their starting Pokémon before a battle.
Maybe this will work, at least for players vs. me: You choose the Pokémon you're battling with first to avoid selective bias, and I'll throw out what I wrote down on a word document, as described before. I don't think there's an organized system for this, but maybe switch outs are only possible in SAFE situations. No mid-move type change to surprise maneuver. More like if both Pokémon aren't attacking and are a decent distance away, and/or if terrain is separating them. Thing is, though, with this knowledge the strategy to just blitzkrieg the opponent becomes infinitely better, in my opinion. They can't switch out in that instance.
Another direction to take it in is that switch outs can be performed whenever, but the Pokémon switching in is vulnerable to attack. So if you're switching out on a live opponent, prepare to take a hit. Thoughts?