I've created a module to add lineage as entity property using hook_entity_property_info_alter. I've done it to add term lineage to search api indexed fields and it worked. Maybe this could be commited to Taxonomy Lineage module? I'm happy to create a patch if so. Unless there's a reason why this was not added to the module in the first place (performance)?

I'm not sure but this could make views handlers unnecessary too.