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.