The key with other theater based attractions is they have a storyline and a fixed schedule where you come in and leave at specific intervals, so they aren't really the same. You may notice that they don't want you hanging around too long in the park retail spots either, they want you to pick your stuff, hand over the cash and get out (or just steps 2 and 3

).
I didn't say there will be "none", as noted in the quote, I said there will not be a flood. There actually might not be any if you think about it. Does ToT sell art deco merch still? Sidenote, I am not 100% sure about the story behind this but at the opening of the DCA version they had an art deco figure for sale (with pricetag) behind the counter at the photo desk. I'm not sure if they took it down, someone bought it, why it was for sale, etc. But anyway, the reason I don't think there will be much, if any, is simply that the merch people have been prone to designs that they can reuse in multiple parks or is printed onto something generic (such as a shirt). I'm guessing crappy picture frames and possibly pens/desk stuff.
Also, nope, I have never sold on ebay. I try to avoid the hoarder mentality that some people seem to get when they become a seller.