Very good point.
I think, for all its flaws at the moment Bitcoin has an advantage over BitShares because they have separate controllers who are well incentivised to manage the security of the system on behalf of the users & are locked in by Bitcoin's supply curve. (So a majority miner can't change the rules without destroying Bitcoins value.) The problem POW has is how to decentralise security & charge much less for the service.
With 101 delegates, BitShares seemed to solve that, except BitShares expects users to manage a complex system, which hasn't really worked yet in practice (voter apathy), especially without any direct incentives to vote vs. not voting.
Once BitAssets go mainstream there will be separation just like in Bitcoin of mainstream apathetic users who will mostly be BitAsset holders vs. controllers (BTS holders) but without being locked into a supply curve like BitCoin, BTS may be diluted to the benefit of the most powerful & active stakeholders.
Your suggestion is a potential good solution as well as perhaps incentives to vote to maximise participation, cold storage voting options (next update
) as well as, most importantly in my view, either mainstream marketed no dilution or a fixed forever supply curve. That way just like Bitcoin, even if there were large stake holder blocks, they couldn't change the dilution in favour of themselves without destroying BitShares' value.