The multiple use items (also works in Ford, Chrysler Corporation products, Oldsmobile, etc) will probably be around for some time but as stocks get exhausted on the more "unique to K-F" stuff the lack of demand will most likely prevent continued manufacture.
This is a hazard that all cars run into over the course of time & why it is worthwile to hold on to older interchange manuals and cross-reference information. You can be armed with good information when you hit the larger swap meets in your area/region and buy up spares to hold on to. If you ever sell the car they are used on, see that they are passed on with the vehicle.
The interchange book I did in the 1990's contains a lot of info from information put out in the late 1950's early 1960's and has been useful for me (including landing 12 P70-FF oil filters from Shell and Conoco which did not have an application list on the boxes).