Valentine is working on getting the shapeshift API in the full node, afaik.
You could copy theirs to make it as simple as possible to also just add metaexchange through the same calls.
https://shapeshift.io/api.htmlIt would be sweet if the you say to the wallet you want to, say, send bitBTC as BTC, and then the wallet automatically gets the rates from every gateway you have indicated you trust through "gateway.com/rate/bitbtc_btc", and then returns those that support it in an ordered list with price and send limits.
Perhaps in the long run its better to have the rate and limit requests be combined, because when markets are efficient every bridge will be able to offer to exchange any amount, but the spread will increase as you need to send a bigger amount.