There should be a middle ground somewhere; some dont want their customs lost or removed, some want to start fresh. I believe its truly in the game's best interests to start over completely: redo Damage and Health systems for cleaner metrics (the way damage works now doesnt make much sense mathematically and only works if you know the game and how the game wants it to work), simplify ability load outs and reduce the overall number of customs. I also strongly believe all existing customs should be considered voided in this new version.
However, I understand that most still love the abilities they've earned and gained over a 15+ year game. That's why I also propose a Legacy Mechanic where the current game is essentially "snapshotted" and bios are allowed to be used in the Battla Arena only along with the customs and skills they have. They couldn't be updated, couldn't add more to it, couldn't create more abilities for it, etc. It'll allow current and older members the chance to still use these characters for fun, exhibition style fights without hampering the chances to actually better the systems that exist as well as streamline rules.
Something that I've thought about to follow this mentality I feel would be executed by simply introducing a new sub-section of the forum titled "Legacy RP" or whatever is desired and perhaps letting that be maintained by an independent team of staff. Far more scaled down than what the base game would entail, of course and only to receive guidance or assistance from the base-game moderation team as said team deems appropriate at their discretion. If conflicts arise, that is for the legacy staff to deal with, if it lacks activity, that is for that section to figure out.
This was a system already seen by the introduction of what was the "My Hero Academia" iteration that was made and participated in by a few members whom also participated in the NWRP as well. While I don't see that sub-section anymore, unless I'm just looking in the wrong places, I do recall observing it and noticing that it had mods that strictly operated within that section; either voluntarily or by simple assignment, I couldn't necessarily tell. But for the purposes of its own independent functionality, it served its purpose at the time from what I could tell.
It's also noteworthy to recognize that "unofficial fights" happen in the Battle Arena all the time despite what a user may technically have access to power/ability-wise or even bio-wise. These fights are generally done in light of "testing out" abilities or whatnot before making an official purchase, but I'd say this same mentality can be applied to all those that want to "retain" all that they have built -specifically with regard to their customs- by participating on an "unofficial" basis. Simply because it becomes unusable in the mainstream due to a reset, does not mean that it all goes away and ceases to exist. Time and place simply becomes more of an emphasized element, rather than "it's on my bio, so wherever my bio goes, it goes" sort of mentality.
Truthfully, what I find ironic about a lot of this discussion surrounding people's desire to live out their personal ambitious growth unrestricted by the rules and directives of the base-games systems is inherently supported and arguably even encouraged by having a section of the forum (which yes, does exist) called "General Roleplay," or even "Konoha Town" itself if dealing with Naruto-centric RP. These sections exist for members to develop their own narratives and RPs as they desire, unhindered by the pacing or direction established by the larger "default" game. While it's arguable that they may be limited to a singular thread per "idea," there may be some compromise to find where if a particular RP develops enough traction, it can have its own "sub-section" made within these categories (ex: how the "Ninja World" section has categories for each continental frame to the verse, such as "Lands of Fire," "The Badlands," etc, so under "General Roleplay," you might see a sub-section titled "MHA RP," "One Piece RP," etc) wherein several threads could be made within to accommodate a particular "General Roleplay" that is desired by an established clique of the community. Which, once again, would be ran by the members of these roleplays themselves, not to necessarily have any particular moderation authority of any kind, but just in a general sense conduct themselves as their own "DM" to these respective categories of RP.
Mechanically a lot of the framework for these things already exists in the current layout of the forum. I think it's just a question of how to organize it in a way that allows users to identify with these sections and not feel that they have to conform to the base game if it doesn't suit them and instead make their own thread among these other sub-sections, separate from the main game.
Sorry to quote you, LoK, and only really address what you were talking about a little then to go off on my own tangent as a follow up.. haha.
