I don't mean to suggest this is something Amazon would bring to market using an Echo. I mean do you really need Amazon/Apple/Microsoft/Google levels of hardware to run a voice interface for an individual's digital assistant?

Is it feasible to install hardware with the capability of Alexa in the standard user's home?

I think the answer to that is probably "yes", more or less. Some things may be a bit harder to do but I don't see why I need a huge black box in the sky to parse my voice or do some geolocation.