don't know about that one, Jimbei and Ace where there and if Luffy were to be imprisoned he'd probably end up in lvl 6 by now to. It's just about how much of a thread the prisoners are and having garp and dragon's bloodline and having helped tons of prisoners escape would most probably get him on that level and he is not a dangerous murderer at all. Not saying anything about a lvl6 prisoner joining the SH's because it could happen but most likely not and the tree or plant logia is indeed quite farfetched and pure fanfiction. Nice idea though but perhaps useless on a winterisland
