This is clearly an attack vector. Chains that utilize these ideas will in the long run be controlled by the few that manipulate the mass media/marketing. Going from objective to subjective consensus is a big step back. It kills the very brilliance of Bitcoin.
51% attack on BTG defeated by a user-activated soft fork providing a check point and hence explicitly banning the attack chain.
Excellent news. In PoS, in such cases the attacker would lose many millions of dollars to slashings/inactivity leak.