That’s why Plasma is built to support different shells, optimized for different form factors which allows to do this stuff like the Netbook shell in the past or now Plasma Bigscreen for TVs or Plasma Mobile for smartphones.

Fairphone have been dealing with this problem of unsupported chips for quite some years now (the hardest lesson learned was probably selecting Mediatek for the FP1) and they’ve become better and better at it - up to the point, that they chose not a mobile, but an IoT SoC for the FP5 for which they got Qualcomm to commit to much longer support than ever before. I don’t see why reason, why they shouldn’t manage to stick to this commitment in this case. On top of that, they’re even working with Qualcomm to allow for replacable SoCs for future upgrades without having to replace the whole mainboard incl. storage etc.

Fairphone offers 8 years of software updates and aims to reach even 10.

It might be expensive when you compare it to the lifetime of a regular phone, but compare it to what you’d spend instead on regular phones within the potential lifetime of 7-8 years of the FP5 (minus 1-2 minor repairs).

zram did wonders back then to the performance/usability of Palm/HP webOS devices, especially the 1st Pre.

If you calculate what you’d spend on regular phones with a 2-3 year lifetime instead of a single one for 8 years (even including a few repairs), it might be actually cheap.