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.