Earlier quoted context omitted.
The iPhone 5s was released in 2013 and it should get iOS 11 this year. The iPhone 5, which came out in 2012, is currently supported. However, it might be dropped this year because it's not 64-bit. Android users should push for longer support. I had an original Nexus 1 and I was quite disappointed when it could no longer be upgraded. It cost me $600.
Aren't we comparing apples and oranges here? This is the O Beta. I'm sure O will be supported on the Nexus 6 once it's officially out.
The situation is pretty complex but the support libs & play services are available on virtually all devices (API 9+ IIRC, but anything older would not be able to run most modern apps).