People already do these informally. Some have gotten flack for it too because it just seems like mostly run by greed and not charity, which isn't so surprising. (Some have rented delegation in the past for this purpose, so the minimum pool idea isn't foolproof). For charities, I've also seen raffles run informally too. It's not that much effort to run one manually, so I do question the value of automating it. And there's also the question of doing so in a trustworthy manner.