You’re not the first one asking yourself this question:
Actually it already came up in 2017:
If you’re looking for official G%§$e approved upgrades don’t expect one for Android 8.
For Lineage OS on the other hand an Android 9 upgrade is already being developed and I’m sure it won’t stop there.
There are also other OSes that could last longer than FP(O)OS (see oslist).
