Yes, it would be great if everything could be upgraded. It's unlikely that will happen though. It might increase costs. The camera module could be upgraded in the Fairphone 2. Also, if you root the phone to install a different operating system, you void your warranty (this was not the case with the previous phone).
Here's some cool news though: Pine64 has just announced that they are working on making one of their earlier laptops upgradeable. They plan to provide a whole new computer mainboard (the one found on their newer and more expensive $200 laptop).

Thank you for your kind words! It is a pity that fair trade products are so overlooked. If they launch it with a Snapdragon 636, maybe it will be upgradeable to Fairphone 4 specs via modules? That would be awesome and definitely worth a higher price.

This is one of the few sites with news on the Fairphone 3. Congratulations!
A high spec phone does not seem to be the plan though. A Snapdragon 4xx series was evoked in an interview with Frandroid in 2017 but it will more likely now feature a Qualcomm Snapdragon 636. This according to blog posts and discussion boards, is an interim phone until the Fairphone 4 which will have higher hardware (presumably 5G).