This page is a collection of questions that occur from time to time
Ubiquiti does not publish any kind of life cycle for their products, but they do publish "Vintage" and "Obsolete" products. You can find those products listed here. There is usually no official announcement to the community, so make sure you check back often.
The Unifi Dream Machine Pro is a 1u appliance that runs the network controller and optionally Unifi Access and Unifi Protect. It's able to provide DPI and IPS at over 1GB/s. The controller can't adopt other sites, and the UDMP can't be adopt into other controllers.
The Unifi NeXt-Gen Gateway Pro is a 1u appliance that is just a gateway. It requires an external controller and can not run any other Unifi portals.