This is a good starting point for exploring improvements. One advantage of DPOS is that you can tweak voting in an infinite number of ways. Besides user reputation, I'd like to take into account the witnesses' track record, i.e. how many blocks they've produced and which percentage they've missed. And while @steemchiller wants to stop witnesses from voting (which would be easily circumvented), I want to give them additional votes. E.g. the top 5 witnesses would co-opt 5 additional witnesses. This would be a way to appoint people who have proven themselves as experts, but aren't rich or popular.

I think experience has shown that a more conservative system would protect us from attackers. This could include a popular vote weighted by account age, account activity, reputation and a follower graph like @steem-ua. It would be difficult and expensive to fake all of those signals.