I wouldnt think it will be that quick because as @dagger212 pointed out, it is used for a lot more than just transportation. So until we address an alternative for plastic, it isnt likely to happen.
Plus even with cars, we will see gas powered cars sold for at least another decade. Considering the age of vehicles, that would still necessitate a need in the 20 year window you pointed out.
Of course things change quickly but humans tend not to. So I think there will be the long trend of adoption.
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