I’m afraid that penalizing proposers for missing bodies may allow a bad equilibrium in which the following happens:
- A single pool of block builders is responsible for a very large proportion of all blocks.
- The pool subsidizes malicious block builders to generate griefing attacks outside the pool.
- Rational proposers notice a large proportion of blocks coming from outside the pool are malicious, and therefore give fee discounts to blocks from inside the pool.
Because of (3), the pool is able to maintain its high proportion of all blocks of (1) and make outsized profits that are more than enough to pay for (2).
It may be relatively easy for a malicious pool to acquire a large proportion of all blocks if it is willing to have some losses to do it, for instance paying 1.03 for a block that generates 0.99 in profits. If this allows the pool to build 75% of all blocks, this will cost 0.03 per block on average. If it then tries to attack 40% of the remaining blocks (~10% of all blocks attacked), this will cost about 0.50 per block or 0.05 on average. So the total cost of running this strategy will be 0.08 per block.
At the same time, rational proposers will now see 40% of griefing attacks for blocks outside the pool, meaning they will become willing to give a 20% fee discout to blocks from inside the pool, meaning they will accept blocks for 0.83 instead of 1.03 (and continue making 0.99 in profits out of it). If all proposers are rational, the pool will now make 0.12 on average in block profits, more than enough to cover the 0.05 on average for the griefing attacks.
The attack may be theoretical, however, because:
- Proposers are unlikely to be rational in the short-term, so the attacking pool may have to maintain the large block proportion and the griefing attacks for a long time before a significant proportion of proposers start accepting blocks from the pool at a discount.
- Other pools will appear and stablish their own reputation for not griefing, but without sponsoring malicious attacks. These may “free-ride” on the fee discounts generated by the fear of griefing without paying their “fair-share” of the griefing costs.
This is analogous to the attack described above in which (if I understood correctly) a large pool of proposers may sponsor griefing attacks in order to discourage competitors. That attack too is theoretical in that competing proposers will just start looking at trusted block builders instead.