The idea intrigues me. Although it is likely well over my head, I find some merit on all angles of the discussion.
I -can- think of several places where a system like this could be viable, I can think of a whole lot more where.. not so much..
Props to you for going ahead and doing the work you've done so far.
I would think that your DEM would be useful for any data-sharing mods. Would make it easier for mods such as Gatherer, GatherMate, Carto_Herb/Mine/etc to all share their nodes regardless of the addon on either end.
I also think using it to distribute updated modules of bossmod addons would be a useful thing. Also, it could be used to distribute auction pricing info from, say the GMs bank alt, to all the guild members, so they wouldn't all each need to individually scan the AH to see price averages of items.. The list of possibilities extend on and on.
However, I also agree that it's a very dangerous concept, and -EVERY- precaution needs to be taken to ensure no bad code gets into WoW.. It would be detrimental to the entire addon community if Bliz decides to shut down addon message channels because of some bad code spreading itself through it's playerbase. (Not to mention the bandwidth that could, conceivable be used by said spreading)
So.. all in all, I say go for it, but don't expect it to be widely accepted until after it's proven to, not only be reliable, but secure. And remember, -your- code is public as well, and if some ill-intentioned genius happens to find a way around your security measures (which happens on a daily basis) We could all be seriously ------- by this addon.