The really interesting dynamic would be if a seller doesn't participate in this program, but its competitor for a similar, essentially non-differentiated product does (or more than one competitor) and Amazon optimizes pricing according to what the non SBA-seller is charging. As sales of the SBA product picks up, network effects kick in for search, detail page carousels, and recommendations to customers with similar profiles to the buyers. The non-SBA seller is forced to manually reduce prices, or lose a huge chunk of market share.

The key here would be product differentiation, reviews, external marketing, or something else to keep sales up. But for sellers competing on price, SBA could be a disaster, regardless of participation.