Lexeme RDF model is described in https://www.mediawiki.org/wiki/Extension:WikibaseLexeme/RDF_mapping#Wikidata_Query_Service
In order for Updater/Munger to be able to consume lexeme data properly, some adjustments need to be made, such as adding types to the dictionary and registering Form as sub-entity for Lexeme.
Maybe also make LabelService to be able to deal with wikibase:lemma predicates.