Why do we need to see these?
For apps to be able to see what query parsers are available.
Any builtin plugins we should be able to just rely on them being there and this just adds more noise and startup costs. Perhaps instead we need a way (if we don't have one already) for anyone (i.e. any kind of plugin) to add externally visible statistics?
It's not really about the statistics for my initial use case - it's about an app pointed at a Solr and being able to discern what query parsers are available.
The main point here, forgetting about numRequests, is simply to have a way for plugins to be discoverable from the outside. This fits in the longer term goal to RESTify all of these things, at least in my opinion, but this is an easy and useful capability in the mean time.
Just wondering why would a query parser (or a highlighter for that matter) need numRequests?
Good question, I wondered that myself when I saw HighlightingPluginBase do this. But I can imagine it'd be useful to see which query parser(s) are being used. One might even want to monitor for inadvertent, or even suspicious, uses of other query parsers.