If a SpanQuery is constructed from one or more BoostingTermQuery(s), the payloads on the terms are never processed by the SpanScorer. It seems to me that you would want the SpanScorer to score the document both on the spans distance and the payload score. So, either the SpanScorer would have to process the payloads (duplicating the code in BoostingSpanScorer), or perhaps SpanScorer could access the BoostingSpanScorers, or maybe there's another approach.
Any thoughts on how to accomplish this? Peter