Now that mostly everything runs with the HB3 (including doorbells), the HB2 is basically obsolete and not needed anymore.
It would be pretty neat if the HB2 could receive alerts from the HB3 (doorbell chime, alarm activation), that way you could have them in different rooms and allow for it to be heard throughout the house on 2 different Home bases.
Adding some integration with HB2 would help save on electronic waste that is just tossed in the garbage (or recycled) since it cant be used for anything in thr HB3 ecosystem.