How would we know, if it’s a surprise? Hahaha
Fairphone learned from its experience with the FP1. As you know, it lacked monthly security updates and upgrades (mostly because a non-friendly SoC manufacturer). For that, they chose Qualcomm for the FP2’s SoC. Thay way they can provide monthly security updates (and they do that for the two official OSes).
Furthermore, they upgraded to Android 6, and after some never-seen-before battle against obsolescence, they fought for providing Android 7. The scene looks quite different from the FP1-era.
(The following paragraph is opinionated because there are no fact about the future)
Android 8 is not guaranteed (official statement quoted above), but you won’t be left back as with the FP1 because Android 7 is still pretty new. At the official Google chart of Android distributions, you can see that up to a 20% of phones still run Lollipop, so app developers won’t ignore 1 of 5 users, because that means a really huge bite to their income. Once the number of Lollipop phones decreases, you still have quite a margin, because there’s Marshmallow in the place of Lollipop then.
But the most important part for me is that you will still receive security monthly updates on your FP2! This is also unprecedented in the industry. Only Google did that in the past with their Nexus and Pixel families, but only for two years.