Are we talking about a Google-certified Android 7.1?
Because a non-certified Android 7.1 for the Fairphone 2 exists since October 2017 – in the form of Lineage OS.
A Google certification is crucial as there are reports of apps (especially banking apps, but also some games) which refuse to run on systems without certification (for example rooted systems or custom ROMs). Even Google nags its users on non-certified systems to go through a registration process.
But if that update is really Google-certified – I will show the greatest respect for Fairphone and will prefer Fairphone over another brands if I need a new smartphone. But as of now, my Fairphone 2 from January of 2016 is still good for a couple of years.