Yeah, sounds good. How would the bonus be divided between the miners? Would it be "fair" to distribute it proportionally each day? I expect this way that if the difficulty changed in the middle of a day that you'd have to split the day into two parts and distribute proportionally on each part.
Not sure need to think about that. One idea off the top of my head would be to track number of shares in the month and the difficulty of each share and divide any bonus proportionally to overall work for the month.
I think better in formulas so something like:
Total Work = SUM(Work Done = (shares) * (difficulty))
"Monthly Bonus" = (total revenue of the pool) - (PPS payouts) - (Pool cost server/bandwidth).
Miner Share = (50% of Monthly Bonus) * (Miner Total Work) / (Pool Total Work)
That may well work but, as you say, it needs some careful thought. If this does work properly then it is a rather graceful way of handling difficulty changes.
Ah well, we can dream.
I heard BitMinter was off to a splendid start with merged mining! Good stuff.