Would this not reveal every importer's gross margin to its competitors? The tariff is only on the importer's "landed cost". If the tariff is itemized(and not just a made up number by the seller), then you can easily work out their gross profit margin and the price they are paying their OEM.
Yeah, it won't last. They'll decide it's too revealing, or too hard to calculate an actual number. People are throwing around all sorts of percentages, and none of them really mean anything because whatever the effect of tariffs is on a particular item, it's bundled up with the inflation that's been growing for years and everyone in the supply chain taking a bigger chunk because everyone else is. This is just performative.
It seems like no seller would want this.