I think we generally agree but I just want to clarify anyways. I'm not saying we should use PNG to store frames from videos.
What I am saying however, is that we should replace PNG with a modern lossless image format that is more flexible so users don't have to deal with these issues. All this colorspace stuff should be automatically handled and I shouldn't have to worry about it not being lossless. If I want to save a frame of video, I should be able to do it using an image format that everybody recognizes and accepts, it should not be a huge hassle and it should be fully lossless.
There's only incentive to do that if the mempool is empty. If the mempool is full, there will be plenty of transactions for both the first miner and the next miner.
Wait... This entire paper only makes sense if the mempool is near empty. If the mempool is full, then there is no reason to mine an empty/partial block because there will always be transactions left for future miners.
So basically: