Is a BIP required for the removal of SegWit Discount for Inscriptions?
The rationale of such a change is to standardize the fee structure across all data types included in a block, ensuring that inscription data does not receive preferential treatment over monetary transaction data.
The removal of the witness discount would be a consensus change, specifically a soft fork. Changes to consensus rules have always been standardized as BIPs ever since the BIP process was created and I expect that to remain the case for the foreseeable future, but this is not a rule; anyone is free to try to convince anyone to run any consensus change without a BIP.
However, I'm afraid you won't have much success with convincing people to undo one of the key improvements introduced in SegWit. For the rationale of the witness discount you can check out these questions and answers to them: