Check this out Alexa Voice Services (AVS)
Looks like all we need is WiFi, mic, and a speaker and we can integrate the propeller with Alexa!
1) Your device captures audio input from a user (for example, "what's the weather").
2) Your device combines the captured audio with the necessary HTTP headers and other information and sends a speech request to the Alexa Access API. The audio should be encoded as PCM16 (16-bit linear PCM) format.
3) The Alexa Voice Service API receives your request, interprets the audio provided in your API call, and handles it the same way it would a request from an Amazon Echo. For example, if your device sent the audio "what's the weather", the service looks up a local weather report.
4) The Alexa Voice Service API sends back a response containing the audio in an MP3 file (for example, the current weather report).
Your device plays back the audio response.