I guess my main hesitation is with prepping reactions before they're ready to be completed. I certainly think in most cases it doesn't make sense but it could work sometimes.
True, most of the time there's no need to start things that you have no intention of finishing right away. But that's perfectly okay, because in almost all cases, %items% will be totally unobtrusive, just sitting in their workshops (while their respective workers are off Eating / On Break / whatever), behaving just like a reaction that got Suspended & will automatically resume when their worker returns. In cases like this, %item%s provide no improvement except for realism: You can now "watch" as the lump of stone gradually takes shape, rather than being able to cancel the reaction at the
very last second & still get back the very reagents you started with. Ideally, you could examine the %item%, and see that "this leather waterskin is about 45% complete", or perhaps even percentage-based
descriptions, like "the sheep wool has been 100% carded, but is only 10% spun."
But, if you wish, you should be able to
order %item%s, paving the way for the aforementioned low-level trainees doing the rough work & their masters receiving the commands to complete the jobs. In addition, this could pave the way for
multiple professions being able to perform intermediate steps: Bronze weapons are
cast, not forged, so why couldn't a %bronze axe% be made by a Furnace Operator, who then hands it to the Weaponsmith to be given a handle & sharpened?