We do some really strange stuff in ToElasticsearch.fromLuceneFilter, altering the boost of a query while we should only be reading information. On top of that, we don't even need to care about the boost, since we are translating a filter, which should not affect the score.
We don't take query.getBoost() into account for some queries, most notably BooleanQuery
We don't translate some easy to translate query subtypes that only affect the boost of their delegate, such as CachingWrapperQuery or BoostQuery
The very last issue, in particular, should be fixed before we address HSEARCH-2208, because we'll have to use CachingWrapperQuery in that ticket.