There isn’t a clear update path on any Android phone. Whenever G%§$e puts out a new OS version they basically decide which phones they deem worthy enough to be able to upgrade.
Afaik Fairphone hasn’t given up on upgrading to Android 7 - and technically it’s possible, see #software:alt-lineageos - but going against G%§$e isn’t easy.
Fairphone is currently rather thinking of going in the opposite direction and making the FP3 another mid-range phone like the FP1, so FP2 owners don’t through away their phones to buy the new model but rather wait for the FP4.
But you don’t necessarily need high-end hardware to upgrade to a newer Android version - you just need to be lucky to have picked the kind of hardware that G%§$e decides to support.
Yes Fairphone is working with other companies and strives to motivate them to change their bad practices.