Thanks for the replies.
Now that you mention it, there is even more that can be ignored, in addition to any state that is identical in previous and current epoch (carried over) , it could also include deleting previous epoch data about any account active in the current epoch because the only reason for keeping the previous epoch is to allow accounts to always avoid reinstatement cost when under 1 year, and if an account is active in the current epoch the reason for storing its data about the previous epoch disappears.
A potential issue is that a miner might be overly aggressive with pruning or not store previous epoch because perhaps the cost of storing the previous epoch immediately / after a couple months will not be worth it and they would rather effectively censor any witness transaction. While storage cost to the miner is pretty cheap, so is ignoring a witness transaction for the next highest paying non-witness transaction. Just ignoring witness transactions and picking something else from the transaction pool will be tiny loss, and witness transactions will be pretty rare I imagine. Might need a way to incentivize the previous epoch to be stored and that incentive mechanism would need to be mindful of not punishing missing data that is pointless to store.
