Really good point.Another way to look at this is using gels in ways besides theatrically designed lights. We commonly use gels for practicals that need to "feel" a certain way in the show. We use gels for music stand lights, footlights, windows in set pieces etc.
Without that foundation of knowledge, you wouldn't know how to color any non-color changing fixture.
I think even when LEDs are common and hung in every theatre in america, there will still be lights in the building that need a gel related solution. Even if it's just in the booth.