When a definition is removed from one Article and placed in Article 100 it often takes at least three Code Making Panels (CMP) and often more to agree to the shift to make sure that the Panels don't step on each other's toes. Occasionally, some people would attempt to revise NFPA "standard" definitions.
I personally hate the idea of Section 500.2 definitions being moved to Article 100 where they will become subject to "refining" by people who have absolutely no idea what they are doing.
How about leaving them where they are, but adding them to Chapter 100 in the following manner, by example:
"Dust-Ignitionproof. See 500.2
Dusttight. Encosures constructed so that dust will not enter under specific test conditions."
At least all the definitions would be located in a known part of the book, even if it's just the listing and an article number. If you try to look up Dust-ignitionproof as the book is now printed, there is noting in either the definitions nor the index that points to Article 500.