While this sounds good, a 25-50% discount is, in many cases, unsustainable. Margins in most businesses are less than 20%, and often less than 10%. In restaurants, bulk margin is often less than 5% (very high margin on some things, balanced by zero or negative margin on others). If the business is a forced seller, say to cover high fiat-only costs, such a large margin is basically impossible.

That said, there are businesses (personal service businesses, consulting, &c.) where there is essentially no margin - it's just time. In those cases such a discount could be feasible.

A business I know about offers 2.5%-3.5% discount for paying in BTC, on top of other discounts (bigger volumes get the bigger discount). This amounts to roughly 25%-50% of their net margin. It works for them, but it is a big hit to keep that up, since they're a forced seller to fiat on their supply side.