Apache Solr is almost ready to support Learning To Rank.
In particular, a Bloomberg plugin to support it is in quite an advance status of completion [1] .
The Solr plugin is expecting the model encoded in Json.
Would be really useful to directly produce the model in Json from Ranklib, taking the writer type ( xml or Json) as a parameter.
I can contribute the Json support for LambdaMART.
Any additional contribution is welcome.
[1] Solr LTR Bloomberg plugin - https://issues.apache.org/jira/browse/SOLR-8542
Sounds like a useful feature.
Will try to add for next release.