I think it might be useful for certain applications to be able to get transaction fees from the RPC API. The problem is that loading all prevouts from disk could be pretty expensive depending on the number of inputs, so it should be made optional with a flag. One way to expose this in the API is to include the prevout (scriptPubKey & amount) with every input in vin, as well as adding a “fee” field to the top level of the response payload.
How would people feel about this?