Sounds like a clever idea !
I had two problems with the content of your ZIP file though.
First, when trying to open Filters.mlt in Shotcut, I got this message:
This means that the .cube file you provided in the ZIP is a copy of the one you used in the template. Different paths.
When I point Shotcut to the .cube file extracted from the ZIP, I still don’t get a green light
Still, the project launches in Shotcut and I can see two items in the Playlist.
But I cannot double-click on any of them OR drag them to the Timeline to display the filters. As soon as I do, Shotcut crashes.
Anyways, when I create my own template using the method you explain I don’t get these problems.
Now, I’m curious to learn how YOU use such a template in another project?
I mean suppose you’re working on a project and that at one point, you need to use one of your templates. If you import say, Filters.mlt in the project using File > Open MLT XML As Clip… >Filters.mlt, you can’t copy the filters from it.
So how do you work with these templates ? Do you start every new project from an MLT file that contains all the filter templates in the Playlist ?