Discussion is moving quite quickly, so I haven't had time to fully think through the game theory, but please give me your comments and maybe build on the idea.
Miner /u/grmpfpff has
stated >There will be a penalty for not including a donation, but it cannot be the orphaning of the block.
In my opinion, their blocks will remain orphaned together with that stupid idea of taxing with obligation the miners who refuse, if they have less than 51% they will lose profits
block is created, cooperating miners would choose not to mine on top of it, but start construction of a parallel chain. Where a second consecutive non-cooperating block was created,
risk of permanent chain split * miners free to create block types they prefer with chance they will be included * persisent cost to those enforcing coop blocks if support is low (risk
tl;dr If even a slight risk to miner a block could be dropped then a non-zero contribution is rational. Feather forking like this also fixes difficulty gaming.