So now that we have negative queries, we don't really need any additional/extra code for facet.missing. It could simply be facet.query=-myfield:*, and that way it could be obtained without getting facet.field results if desired.
Of course we would need to enable zero-length prefix queries in the SolrQueryParser for that, but I think we should do that anyway. So should we deprecate facet.missing, or is it only really used with facet.field queries, and often enough we would want it *in* that list? -Yonik
