I'd rather change the entire persona. Alexa, siri, google, etc are all bland and boring. Not surprising given the creators. I want a sassy NeNe Leakes!
I mean, Cortana is a little fleshed out... Although but I'm not sure she a sexy blue woman appeals to all
I like to envision her as Zoey from Left 4 Dead.
If you make your own Alexa device you can do so. It's simple enough with a Raspberry Pi and a microphone. Unfortunately you lose the far-field mics is you do this.