I have an Idea.
Fairphone could developing new Modules for the FP3(+)
A new Display Module: something better than Ips maybe Amoled Display. When the actual display costs around 90€ Fairphone could set the Price for 100€.
New Speaker Module: a speaker module with Dolby Sound. To have the Dolby Settings Fairphone could bring an Update for it.
These are the 2 Modules that i think could be best Upgradable as the other Modules.