or if it MUST be deprecated, give a warning for at least one update in advance when the filter is used: A pop-up that shows up when using a filter that will be eliminated in a future update that says the filter is going away, and which can be dismissed with a "don't show again" option.
I sort of agree with the intention of this soft, warn-in-advance approach but in reality it makes little difference in my experience.
If the feature exists it will be used. If it's removed, users who used it in previous versions will scream that they did not know it was disappearing.
Warning dialogues about future feature deprecation are usually dismissed without a second thought. I doubt they prompt anyone to plan an alternative future workflow without that feature.
Good idea though!