I looked at this earlier this year. Lack of API access means that we cannot build an application similar to Simple in the UK. I e-mailed several banks and most of them did not reply.
My understanding of Simple is that the services they provide are simply provided by their partner bank, http://www.thebancorp.com/, which is a regulated financial institute. I'm not sure how the issue of API access is relevant but this may be my lack of understanding more than anything.
Real shame, is there a blog anywhere about the setting up of Simple? The idea is brilliant.
I believe these guys are working on something similar:
https://holvi.com
I don't know if they're planning to offer a debit card though.