I think unless advertised and/or approved as an official partner website, the playerbase would have a hard time picking up on the site. Mostly because the playerbase is small as is.
But if it could get a sticky thread under a trading forum, then this could be huge.
The only downside is, why trade when you can use Marketplace.
I think one thing that would be more interesting would be a website that tracks the cost and quantity of each card (BFP) by day, week, month, year. Like on this website (This website is for world of warcraft items - example): https://theunderminejournal.com/#eu/twisting-nether/item/159125
