Yes, because we may need to be able to quickly change the criteria, we may find that sometimes feeds contain bad data that needs to be filtered, exchanges go down, etc. etc.
For that I prefer to have multiple feeds and be able to say with confidence - this a very good price approximation.
But I see what you are saying - this is brainstorming, and if you decide to go that route, it will be in the RPC, since it is how everything else works.
So then a hybrid model as BM proposed would work:
1) Limit fluctuations to 50% range in 24 hour period (or less decided by the delegate)
2) Additionally allow delegates to exclude transactions based on their own criteria via RPC - I see BM's point that all it takes is 1 delegate to still be able to get their transactions in. But I think that should make it a bit harder to manipulate the market.
I think 2) is still good to have even if you don't see value in it initially. Imagine we experience some abuse, we might be able to very quickly deploy a patch and recommend community only vote for delegates having such and such filter in their system, until this is resolved. The most responsive and flexible delegates will win the community's hearts.