There are graphic design template sites all over the internet. So obviously there is a marketplace.
No one wants your mundane layouts via NFT. My SOP on typical design work is, if I can’t copyright it, it can’t be NFT, which is being used for one-of-a-kind things. Besides, if you are designing stuff particular to some other entity’s branding campaign, it isn’t necessarily your content to start with and layout shells are impossible to copyright.
NFT might be useful in stock imagery. But, at this moment in time, is the effort worth the return? High Art that commands a High Price, maybe, but not a $30 photo asset.
No, I haven’t thought about it beyond that, and my initial take on it was pretty much one of disdain. Trendy tech tends to go the way of all trendy things. Eventually. Or not. 18 years ago I thought flatbed print machines were silly too and look where that is these days.