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If you're gonna allow tricky bits, keep them in SBK, copy WSBK rules exactly, even the "EVO" class if you want but stay away from drafting your own stuff for chrissake.
Zero wrong with a 600 "supersport," class... something that would allow any commercially available "add on" type electrics (like Bazazz, etc.) that work with the stock ECU. No full ECU swaps and standalone management allowed. If WSS rules aren't good for that than look to BSB or somewhere else that has a 600 class with rules geared for parity and low expense... Like keep the bottom end stock, allow for +1mm pistons (only for those bikes not currently overbored, like a 640cc limit for OEM 600cc bikes), etc.. Allow some minor head work, stock cams (adjustable cam gears?), bladda bladda. Something you can reasonably build for $10-15k (engine only) and go nuts.
The final class should be either Moto3 rules / format or akin to CCS Lightweight Supersport. Something for younger riders to easily get involved in and keep the machines as close as you can spec wise. Done and done.