I don't believe the exact nature, scope, cause, or extent of the dust "issue" is generally known--except maybe by Nikon. And, they ain't talking.
You can read all sorts of speculation and conclusions about it on the internet. Some say it's dust, not oil. Some say it's oil, not dust. Some say it's both. Some say is dust introduced at the factory. Some say it's caused by friction between xyz parts. Some say it's excess lubrication being flung. Take your pick.
Some seem to say it diminishes with use and time after x number of cleanings or shutter actuations. See the link I posted to Lens Rentals elsewhere on this forum.
Here's what I would say:
If you are concerned enough about the issue and you don't *need* a camera right away, hold off until you get enough reliable information to satisfy your concern.
If you need or just gotta have the camera, then get it now. Also get cleaning supplies and be prepared to use them.