Proof-of-stake has progressed quite a bit since that document was published in 2016. For example, nothing-at-stake is fixed by slashing stake when anyone submit

Proof-of-stake has progressed quite a bit since that document was published in 2016. For example, nothing-at-stake is fixed by slashing stake when anyone submits a proof that the staker signed competing branches. (But I agree that Bitcoin is unlikely to change.)