Why did you mention Shapeshift and Evercoin in your Whitepaper? Do you have a cooperation with these projects?
The fees for using Bitcoin, for example, would be exorbitant because it would include fees charged by either Shapeshift or Evercoin, but only in the beginning.
You are right. Even the Ethereum gas + your own (Rockstable) fees, may seem too expensive for some users. I hope it not will be a problem.