A proof-of-work or proof-of-stake system are the only known ways to stop someone from running a lot of client peers or hatchers in a decentralized system in order to block transactions or double-spend. I do not see any new solution to the Byzantine Generals problem in your answers.
Or a system of "elitist" "miners" who have to share the work cooperatively, like I proposed here:
https://bitcointalk.org/index.php?topic=220513.0But nobody seems too pleased with that idea... :-(