Major Description
The filter->query migration might be a bit trappy in terms of performance for our users.
For instance a FilteredQuery over a TermQuery and a DocValuesRangeFilter should be migrated to a BooleanQuery with a MUST clause for the TermQuery and a FILTER clause for the DocValuesRangeQuery. Performance will be similar since in both case we would use the query to drive the iteration and the filter would only be used to check documents that match the query (we would NOT try to advance the filter iterator).
However, if you only go half-way through the migration and end up with a FilteredQuery over a TermQuery and a QueryWrapperFilter(DocValuesRangeQuery) then performance will be terrible because this QueryWrapperFilter does not support random-access (which is the way such filters were not too slow before) and hides the approximation support from the DocValuesRangeQuery.