I guess that's the real estimate though. I can talk for Sailfish I have been working on, the UI is running as proof-of-concept (and there was a video of it), but getting it to a usable state is a much more effort.

Recently two more persons got involved, and we are working to redo the base in a more sane and maintainable way, then we can process with getting more of the hardware enabled in Sailfish and polishing the port.

As for dual-boot, it seems technically possible to me in the same fashion as Gemini PDA (multiple boot partitions + selecting the one to boot from at device startup though key combination or menu). However, don't take my words as confirmation, as there might be more difficulties with modifying bootloader of retail devices ("thanks" to Secure Boot) compared to development prototypes.