I feel it was worth posting in any case. You may have already known this information, but those viewing your post may not have.
System seems to be set up pretty well to balance chests and keys, if you invest time into the game.
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If you want chests, play in a premade. If one person gets an S everyone in the premade does, if you haven't already gotten a chest on your champion. This makes it fairly easy to quickly acquire chests if you and your premade have a diverse champion pool.
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If you want keys, play and win more games. This is the time investment, key fragments are the reward for consistently playing the game, as the only dependent is winning games.
Your suggestion of being able to trade keys/chests could create a situation in which you (or a bot) could just grind games for free content. I believe this goes against the intentions of why hextech crafting was implemented, being a system designed to encourage both good and consistent play.