Filament directly from bottles

Has anyone experimented in this area?

Free filament

It seems to me that I could use this device to create plastic filament which (although rectangular in cross-section rather than round) could be fed directly into my 3D printer's standard 1.75mm extruder + hotend?

Or that it could be used to produce (e.g.) 1cm wide strips of plastic to be fed into a custom-made extruder (rather than pellets) to make 3D-printing filament?

It is interesting, but I forsee a couple problems. You don't know if the bottle is uniform in thickness and you can't control the width of the strip very accurately. If the plastic strip going into the extruder varies in cross sectional area (width x thickness) the rate that the plastic extrudes will also vary and that will result in poor print quality. Finally, printed parts will be limited by the amount of plastic you can strip from one bottle unless you figure out a way to join multiple strips together end to end.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Feeding a pet string made in such a way directly into an extruder would be super. It just won't happen tho, such filament is too soft and you won't be able to rigidly push it donwards into the nozzle.
I've seen experiments, to which I cannot provide the link alas, where the author folded a larger string in two along its axis, to make it thicker and stronger, and pushed it by hand through a heated extruder. It did extrude, but was hardly manageable, plus you need to device a motorized feeding method.

Producing proper filament with a DIY method is also totally an ungrateful project, here's my results: [www.ephestione.it]