IMO all witnesses should provide feeds that are based on the same underlying principles. It is a good thing to define these principles in the form of BSIPs, and let the witnesses handle the details themselves.
For example, if some witnesses follow BSIP-42 and some don't, there is the danger that the median feed jumps back and forth between two values that are relatively far apart. This would probably disrupt the markets and would also increase the danger of a global settlement.
True, this happened earlier when some witnesses were providing crazy high feeds and some were providing normal feeds. There should be some clear consensus on what the terms "feed" and "mssr" mean. I think mssr is quite obvious, but feed had recently been redefined to something else, which is dangerous to the system
EDIT: Actually, if some witnesses disagreed with BSIP42, they could feed much lower than the "normal" price to offset the high feeds. This is the meaning of decentralization. You are still correct that the feed would jump, but this problem is solved by having more delegates
Unfortunately its not. Because there was plenty of examples where witnesses would be voted-in by specific proxies and then they would have to comply with proxy terms of price feed (how bitUSD met blackswan). So, more expense to the blockchain that will not provide variety (as you suggest) of price feeds, but even more establish centralization of individuals is not a solution in my opinion.
Quite correct in mathematical way that more delegates would be solving that, but IF they are only independent from sometime very wrong proxy request or to define more strong BSIP on limits of the feed configuration so they can all apply to the same matter. Now only first case where independent witnesses would be really decentralized, the other one is just again delegated and i don't know why everybody has a problem with it.
dPOS is not decentralized proof of stake, but DELEGATED one. Proxy delegates tasks to a witness. Witness delegates blocks to the chain. Committee delegates fees to the chain. Etc.
In my personal (non-biased) opinion - it's not a problem of technology, it's a problem of human error and inability to agree/unite as ecosystem --> hence why BSIP has to be written and in both cases (goes good or bad) - its well documented.