I've often thought that the easy way for them to at least offer a preview would be to just create a category on the Calamity Salvager (or similar) that lists all the cash shop items, but for some non-existent currency. Then you could at least use the "Try On" feature for each of the items. It's not a perfect solution by any means, and the fact you can't buy it there would require an explanation, but at least it could be done with very little/no programming effort.