I'm with spartacusrex. The ultimate test is for someone to pull of one of these (theoretical) attacks and catastrophically and irreparably damage the network in some way, or at least prove that one of the attacks can be used to consistently and successfully attack the network and/or individual users. Until this test is completed, I'm going to assume that POS and other variations (DPOS) is sufficiently secure.
Also, it would be in everyone's best interest if POS was broken sooner rather than later while valuations are low. So please, if you have a guaranteed attack, go ahead and do it and prove POS useless.
I'd expect this happening only if there IS already multi billion business available to attack.... as usually always too late.
My hope is - and thanks to TPTB - that here is platform to elaborate on this issues in public, cause that's the risk managament we all can afford.