Is it at all possible to import/export filmstrip files?

In case you don't know what they are here's an example of them being used

No there is no such possibility.
However with melt you can convert an video clip to a series of images (one image per frame), then edit them and later import them using kdenlive's slideshow function.

But the possibility to have everything in one image and not having to edit every single frame would be a nice function.