If Twitter could use common standard like microdata (proposed by w3c), it would probably be a better approach.
The big problem with Twitter product cards is the lack of real time information (ie the data shown to user is crawler dependent). So, e-commerce vendors with dynamic pricing needs (like hotels, airlines) wont use it much. E-Commerce vendors (like Etsy) where users are little less price sensitive have a better shot at using these cards.
