Sam, i maked a track with solution https://tracker.moodle.org/browse/MDL-60759
Apache Solr 7.1.0 was released not so far away (Nov-2-2017), so there are only few users of this version at the moment. And they maked Trie* types as deprecated against v6 or lower: http://lucene.apache.org/solr/7_1_0/changes/Changes.html#v7.0.0.upgrading_from_solr_6.x
You can take a look for track with solution