I don't see why it has to be a big issue in the manufacturing, it seems to me it could be easily incorporated into the current design simply by creating a single new part that would take the place of the current press-fit bezel. The only difference is that the new part would extend past the front of the light and hold the threads for filters and/or lenses of various angles.
Admittedly, this still leaves the issue of the quality of the fitting of the new threaded bezel unaddressed, but it would be the quickest and easiest solution to the problem. Further, if the thread diameter was made to match that of other similar lights on the market, namely the Spark products, then it adds to the appeal of the design change because anyone with Spark accessories could also use them with their ZL, and vice versa for any accessories ZL were to produce. They're similar enough as it is to reasonably assume they're made in the same factory, so it shouldn't be a big deal from a manufacturing standpoint; the only issue would be getting Spark to agree to let ZL use their same sizing conventions.
Of course, a better solution would be for the emitter housing itself to be threaded to allow for completely different bezels to be fit to the light. Not sure if that'd be an increase in manufacturing R&D and tooling to make happen or not though. I think it would also represent a potential for compromising the light from user error, and ZL might not be willing to open themselves up to the issues that would come up from someone messing up their light via user error, and expecting ZL to replace it as a result.
In short, I would be very interested in being able to have a threaded bezel, particularly if a set of aspheric lenses with different diopters were available so that you could tailor the width of the beam to your taste/needs. And, a true deep red filter for astronomy would also be much appreciated by me as well.
