Yes there are roms that are made available by Dev communities such as XDA and it seems that some devices have received support many years after they were done.
The Galaxy Nexus is an example: http://forum.xda-developers.com/galaxy-nexus
I think it's also worth noting the two years of support isn't new, but Google was announcing a guarentee of 2 years of support for the OS and 3 years of support for security. I previously had a Nexus 4 and it stopped receiving the new OSs about 2 years in.