The doorbell software on these cameras is very weak and in no way comparable to other products on the market.
A real game changer and something none of the competition have would be SIP integration. I could then link the Doorbell to my own SIP client which many phones integrate into their handset (saving you the development)
It also opens the possibilities to business markets as the door bell can be used as an intercom system with most business phone systems.
SIP fully supports video and you should look at the AXIS 8105-E device for inspiration