From Does the FP2 with android 9 upgrade get security updates? - #7 by ontheair
Fairphone said that the FP2 will not get another version upgrade, so Android 9 will be the last official Android version.
As far as I remember they did not really say anything about how long they will provide security updates. But I guess there will be security updates as long as Google will provide them. This should be until September 2022, then Android 9 will be EOL (according to several online sources).
Imho it could be a new device. But which technical features would it have? Maybe it could be comparable to an unfair produced phone costing 450€.