But wouldn't that only affects if they somehow kill my target then? Suppose all the goblins go after me but a player goes before I post my action, the player later posts his, he kills the goblin. Can't I just edit my to target someone else them?

Example:

"Roan attacks gobling 1" to "Roan was going to attack goblin 1, but he was slain by X so instead he quickly changed his attack to goblin 2."

I can understand how this wouldn't work if one of the goblins go first.

Edit: And shooting at meele could be an issue but then can't I just add the -4 to the roll if that happens?

Edit2: Seems like initiative tends to be an issue on play by post roleplays, if we all roll for it and wait for all the numbers won't that drag down combat?