I have a few modules that were created specifically for filtering purposes, but after some time I can't remember whether they are really and still in use for filtering, therefore I don't dare to delete them during a model maintenance/clean-up process.
I can see that those modules/line items are not used as a reference in any other line items nor published to a dashboard, but is there a way to make the same check and verify whether they are actually used for filtering or not?
Sadly, there is not a way to identify if a line item is being used as a filter or not. The best, and only way I know of, is to use the Notes filter on the filtering line item ("used for filter in XYZ view). And to be honest, this will be more complicated with UX and custom views.
I believe it is a common issue, especially with custom views for UX. I am not sure there is anything coming, but I can check but I seriously doubt it. The problem with views are they are dynamically created/read and are not in memory like a module/list/line item, therefore they are difficult to track.