It's pointless to talk about creating an open-source version of Siri or Alexa unless you can explain how you're going to also create and maintain the server-side infrastructure needed to make it work. The Siri and Alexa interfaces may run on a client, but they're brain-dead without the server farms of Apple and Amazon behind them.
A similar example from the not-too-distant past: Aaron Swartz's download of a significant chunk of the JSTOR database. Those JSTOR articles wanted to be free, right? And they were set free - copies of Swartz's JSTOR download were available in a multi-GB torrent on several sites. Swartz's entire rationale was that those articles should be freely available to everyone.
So where is the free, open-source version of JSTOR today? It doesn't exist, because building and maintaining a server-side infrastructure that makes that database useable costs money
Solve out the server-side economics, and you have a shot at building an open-source Siri. Until then, you're better off putting your open-source efforts into client-side applications.