My gut reaction to this was “why bother.” But even if a pathogen isn’t spread via toilet water aerosol today, it doesn’t mean a new pathogen can’t emerge that could use this transmission vector in the future.

That said, a virus that spreads in this manner should be containable by having some kind of sterilization agent in the toilet water (already commercially available products you can use that adds bleach (or similar) to the water. Typically a slowly dissolving brick of chemical added to the back of your toilet