Bitcoin lightning POS support at major chains like gas and grocery, where liquidity is handled by the wallet providers and routing has a nearly 100% success rate(like inside a lndhub hosted wallet) and in under 2 seconds. Auto-conversion to dollars at the retailer would also be necessary for accounting(like strike/taro) Retailers would have incentive to push this to reduce their banking and payment processing fees. This service would need to charge a 0.25% or less fee, end to end.

A bad first pass idea could be: Something like this might be handled by a funds confirmation and payment committment that is made at point of sale, and the lightning transfer happens later and in the background if routing liquidity is a problem. The issue with this approach is it involves temporary credit and therefore KYC for a trust relationship.