I also am using a Volara. And I also had the cup deform in baby bottle sterilizer. I've been told that it has been used for decades in hospital settings and was introduced for home use a few years ago. I can't fathom why sterilization hasn't been addressed, especially given the price.
On the other hand, how much of a risk is there for the air tube becoming a place for NTM to grow? Air goes through it in only one direction - towards your mouth.