First thing that pops up in mind is : where will the Steem be taken from ?
You have to setup some kind of Steem wallet account. How would this account be provided with Steem ? Derive part of Steem Curation or Author money ?

Also I suppose if you want to make a credit card service you have to register it somehow on some financial institution. Where will the fiat money go ? You have to setup a bank account.
I guess every time you set a link to fiat, you have to follow KYC/AML rules (see crypto exchanges where you can get/send to fiat).