Hmm yeah that's probably a workable idea and should be pretty easy to implement. I can look at adding that... where should that be added into the API, in your opinion?
I'd include it with all the other block stats, another field alongside shares per round etc.
Edit: Thinking about it a bit more, I realise this wouldn't suit pools with more than one reward method, eg both DGM and PPS since the block reward would go to both and the estimated fee for the luck based reward method would be too high.
So I think one field recording the total income per block (including txfee and altcoins valued in BTC) and another field recording the fee (as a decimal number) would be necessary.