Rational
Current sale_supply module add “sale_supply_on_sale” in product but isn’t configurable by company (multicompany)
Proposal
Use MultiValue in supply_on_sale field
I do not think it will follow the general pattern of product’s fields in Tryton. Most of them are straight on the product/template like salable, purchasable, lead time etc.
As most of those fields are just referential data that are duplicated or used in computation on operation records, I do not think we should try to support all cases in standard. The special cases can always be managed with custom module and the supply_on_sale is no exception.