First, thanks for your opinion Hive account@valued-customer , I felt this post was just too large as a comment at The History of Delegated Proof-of-Stake

I think, every system can be attacked (51% attack on PoW, etc, etc). Regarding REP what I find interesting is that it doesn't have any witness power value at the moment and it is part of the system for some time now. That is an advantage in my opinion. Outsiders can't just create REP in a minute and take the whole chain (like Justin Sun suckpuppets did). If STEEM had a REDPOS protocol, he would at least needed to start a "stealth" attack first (create the suckpuppets and "work" on them to adquire enough REP to guarantee a good witness rank).

Also, in my opinion, a good REP system, should take the account age as parameter too. That's the advantage of a 4 year old blockchain (you can't implement such a thing from day 0, but we are not on day 0). Why would a "baby" represent "adult members" of the chain?

The chain is only 4 years old I know, but it is still better than 0. Maybe if the chain was 40 years old, should ask for a 10 year experience as parameter to become witness. If the chain is 4 years old, at least 2 years. Something like that, the idea is that you need to hang around some (significative) time to become a witness on the chain.

For a social oriented blockchain, I see the "REDPOS" concept as better than "DPOS".

After all when STEEM started it was announced as "experimental POW" with a 1st failed attempt:

[ANN][STEEM][POW] - An experimental Proof of Work blockchain

and here the "good" one:

[ANN][STEEM][POW] - NO IPO | NO PREMINE | NO INSTAMINE (relaunch)

So for a REDPOS deployment, the advantage is that witnesses didn't know their REP would be used, we could argue that they were "mining their REP" during 4 years.