Since it is possible to upgrade (community Kitkat port) I trust Fairphone that they will do everything they can legally do to provide an official upgrade to Kitkat for the FP1.
And even if not, one can follow the tips for improved security for the FP1(U). (There has been a lot of discussion about security already. I’d like to ask you to read through the forum a bit, if you are interested. 
)
But back on topic: I’ve read that other phones with the FP2’s Snapdragon 801 have received upgrades to Android 6. Additionally Fairphone promised to release the source codes, so even if they cannot provide an upgrade themselves, the community will be able to do so.