Remember that Fairphone made a deal with Mediatek to get the source code of the FP1’s SoC and worked hard to update it to Android 4.4, all of this after the phone was no longer sold (they finally developed a 4.4.2 alpha, all working fine but the Bluetooth had instabilities because of Bluetooth LE, so they couldn’t release it as stable, although most people in this forum use it as a daily driver).
Based on this experience, and knowing that Snapdragon SoCs are more open —source is published at CodeAurora.org by Qualcomm themselves—, some of us probably expect Fairphone to support the FP2 after its commercial life with security updates for Nougat —as long as they humanly can—, and until Qualcomm stops shipping code updates. That could make 5 years into nearly 6 (security updates only), which is three times (!) the industry standard (Google Nexus/Pixel phones and Android One).
Fairphone could be critisized for some things (I strongly did it for some time), but not for abandoning their phone models, gosh. Learn about how mobile OSes have been designed for obsolescence and then look at how Fairphone is fighting against a quite big industry.