I've been thinking that - very similar to your idea - it would be very useful to allow assemblers (and other buildings) to accept higher-quality ingredients, treating them as the lower-quality ingredients needed by the current recipe.

Something Like that would also work, I picked inserters ...

You can just filter the output inserters on your first quality machines to shove higher quality outputs into a box for later consideration.

That's not really a solution. It's kind of naive to assume that storing your excess uncommon grenades for future use will ever actually end up being useful ...

I know quality is a very talked about mechanic, and similar solutions like allowing assembly machines to accept mixed quality or buffer all qualities have been discussed. I think those both have flaws and exploits that don't make them ideal. Personally I think the core of the quality system is ...