The basic idea is that because while towny is a great mode of playing, you lose the inherent thrill of "living off the land" type of gameplay you encounter in single player. There is something fun about having to memorize your base while you're hunting for meat, or you're doomed to spend the night in a hole to avoid dying for the first while. Satisfaction from getting your first farm going, a reliable source of food between day/night. Like skyblock, the thrill is in the challenge. On that note, that is why ideally this gamemode would work best without meebles, or donor perks, etc.
To clarify: There will be very little rules in comparison to towny. Griefing, killing, and all those nasty things will be legal. This would be an entirely "at-your-risk" game-mode, and like life, at some points may not even be fair. :) The challenge, and arguably the fun is that very hazard, having to identify your enemies and friends, team up with friends against enemies.
Additionally, I also believe that Onis is on board, however it's in the line to be done. I'm not sure if this is a follow up, a re-suggestion, or something else?