Hi @Alice, welcome to the forum! Why not introduce yourself here? 
I’ve moved your post to the Road Map category, as I think it fits here best.
I see two reasons for the FP2 becoming obsolete:
- Software support ceases. At some point the chipset manufacturer (in our case Qualcomm) just doesn’t provide appropriate updates anymore (as seen with the FP1). In consequence some apps won’t work anymore, if they get updated, etc. Also at some point it will become uneconomical for Fairphone to provide security patches (we can hope that the open source community can hop in and step into Fairphone’s place).
- Impossibility of producing spare parts in small quantities. Low prices live from high production quantities. As the years go by, demand for spare parts will become lower (because people get a new phone instead of investing into spare parts*). So in consequence Fairphone will not be able to produce spare parts anymore for a decent price.
So in conclusion: If spare parts are still available in 7 years, the phone will not be less usable (as in “use it as a phone” and not as in “use it as a gaming console”), but it might be less secure and some apps might refuse to work.
* the main board is 314 € and people will weigh up weather to buy a main board for an old phone or get a new phone)