For now, they are most likely going to run it like a standard credit card, which means 18-21% credit. But if you pay your card off every month like I do, interest isn't an issue. The card would be a benefit to me by allowing me to consolidate purchases into one bitcoin payment (lower block fees) at the end of each month.
If I couple that with spend and replace, there are little to no cgt.
It's hard for me to see the downside.