I wont deny that private sales happen at gun shows, but I don't think it's what it's made out to be in the media. When I was a NR working in TX and had a TX issued concealed carry permit i failed to meet anyone at a gunshow that would privately sell me a pistol i wanted. What is the proposal to "close the loophole", making it illegal for non FFL's to display firearms at gun shows or require universal background checks? If it's the latter, "the gunshow loophole" is a misleading buzzword.
The closure is to ensure simply that all firearms sales at gunshows must go through the NCIS background check. States that have implemented this also provide the set up and people to process those checks. Whether or not that works, I don't know.