What you are proposing is raising the upper peg of the HBD. The upper peg is more important to the chain than it might seem.

1 HBD is always $1 in the perception of the blockchain. So when HBD is trading for $1.25, Hive blockchain still prints HBD assuming the $1 rate. What does this result in? Overinflation of both HBD and HIVE by creating a fake haircut limit.

This fake market cap situation happened on Steem when the SBD price went up to $10-$15. The actual market cap of SBD was 10-15 times bigger than the internal market cap for SBD. When SBD hit the haircut limit at that point, it was too late. The excess SBD got converted into STEEM and printed 10x more coins than intended. As a result of the excess printing, STEEM and SBD both experienced a downward spiral that tanked the price of both tokens. SBD was under $1 for months and STEEM dropped to $0.1 during that time. It took 3 years to kinda recover from that. I would say HIVE price would be much higher if we didn't have that overinflation in our history.

We implemented HIVE to HBD conversion mechanism to help the upper peg and not have that shit show again hopefully.
Edit: I wrote this thinking the proposed fee is on hive => hbd conversion. This comment doesn't make sense otherwise.
Edit2: A fee on HBD to HIVE is meaningless. You are changing the peg from $1 to $0.75 essentially.