Bitcoin was created to avoid bank taxes and stuffs like that and now we can see a scenario in the future where the fees value can be a problem. That's ironic.
I don't know about the limit, maybe it will be a common sense, people will stop to make transactions if the price goes too high so in that way everything will go be more cheap.
I agree and bitcoin's decentralization feature attracted online sellers for that idea and for security too. If the fees are higher,it became the same as other sites which charges higher fees. I hope this is not the scenario in the future.As of now,fees is still cheaper.
Your hopes will be broken for sure because transaction fees would surely rise up on the long run because of bitcoins adoption so this means miners will surely put up some price on every transaction because they are making money with it. At first this is why i love bitcoin because of its low fees but considering they will increase i dont think it will hurt because its only a small amounts.