The subsidy is currently 5,000,000,000 units, giving you a lot of dynamic range to play with. That will not always be true. And rounding to the "nearest" satoshi can be gamed, for trivial gain at first to be sure.
It is obvious to me that by the time the generation reward is significantly reduced, satoshis will be split so what is now known as 1 bitcoin will be more than 100,000,000 atomic units. Even in the highly unlikely case that a satoshi will be significant, since the value is rounded down, this will only create a preference to weights which result in an integer, which causes no harm.
Once again, implementation should follow design, and the "2.1E+15 atomic units" detail can be changed.
You are probably right about that.
Oh, but did you notice that you changed your scheme already? From "round to nearest" to "round down". One of those was probably just a silly mistake, the sort that happens to everyone from time to time. Simplicity has a value that is hard to quantify.
Also, I'm pretty sure that your idea will create total chaos. Not less forks, but more. Lots more. Like on nearly every block. Not at first, necessarily, but as the subsidy shrinks relative to the transaction fees for sure.
Did I say it will create less forks? I predict that the equilibrium found will be less than 10 minutes, which means more forks.
I doubt it will be "on nearly every block". As I explained, if it comes to that, miners will choose a larger weight which decreases their invalid rate.
Actually, miners will choose the weight based on whether they got the last block or not, and whether they are getting paid kickbacks to support/override blocks from the previous miner. For most miners, I think the best payoff would be prevDifficulty+1, except when they are working on extending their own block, in which case it would be the minimum, or close to it. The exact game theory optimum would depend the acceptable range.
I didn't talk yet about how to handle transaction fees, so you may want to defer judgement until then. Hint: You won't be able to get the entire fee of all floating transactions by creating a very light block.
Oh?
Option 1. You pay "easy" blocks less and put the balance into a fund used to pay extra for "hard" blocks. Equilibrium at 10 minutes, which is what you wanted to avoid.
Option 2. You pay "easy" blocks less, and the remainder carries into the next block. Equilibrium at X minutes, which is no more optimal than 10 was.
Option 3. You pay "easy" blocks less, and the remainder is lost. Equilibrium at 10 minutes.
Option 4. You pay "easy" blocks less, and "hard" blocks more, creating money out of thin air. Equilibrium at whatever the weight cap is.
Did I miss any?