This is easier to say as Fable is good (even SOTA). But people have been were saying this continuously for the current model and for now the improvement are still coming.
A better question is would you settle for o3 now or pay 20$ or 200$/month for fable ? Because o3 quality is available OSS.
It is like the new IPhone, in some sort. At some point come a feature many would like to have, despite diminishing returns.
We will see how long labs can keep up and what the scaling curve look like, but I would be more worried into losing sota status to Chinese companies than letting them take the open non-sota approach.