The real Linux aspect is definitely something that many developers find appealing. I still meet a lot of hackers who couldn't think of using anything else than the ageing Nokia N900. Hardware keyboard, Debian packaging, root out of the box, ...

For this group something like Jolla's Sailfish (see http://bergie.iki.fi/blog/jolla-sailfish/) or Ubuntu Mobile will be very appealing options.

Disclaimer: I've worked with some of the people behind both Sailfish and Ubuntu Mobile back in the good old Maemo/MeeGo days.