I'm currently working in a project that integrated with iOS Passbook application to deliver digital passes to their users. Spent some time in investigating the changes to passbook application in iOS7 (beta 4). Here is a quick summary of it.
Apple listened to its user's feedback and have come with some features which increases the usability of the application.
Add multiple passes to Passbook.
Yes, you can able to add multiple passes to the Passbook application in one go. So, if you are issuing multiple passes to your users, probably have a page with all the passes and you can have download all link, which downloads all the passes in one shot.
Delivery through Barcode.
Apple have added one more delivery mechanism to the passbook. Currently you can deliver a pass through Safari browser (with vnd.apple.pkpass as header) or Through email attachment or to stream from your native iOS application. Now in the new passbook app they have added a barcode scanner. So the content of the pass can be crisped into a barcode and can be delivered to the Passbook application.
Anchor tags at the back of the pass.
Currently you can have links, but you cannot have link text. For example if you want to link http://www.google.com to 'Click here' it is not possible. But it will be possible from iOS7
Expiration date for Passes.
Now passes can have its own expiration date. It's a meta data that you can set and after that the passes will be destroyed from the Apple passbook automatically.
Usage restriction by Geo location.
You can restrict the usage of passes, within a specific geo location. For example if you are issuing a coupon, then you can make sure that your users could able to access the coupons within a specific geo co-ordinates.
All these are nice features that are provided in iOS7. So far i was happy with all these news, until i read that, (Dev forum link)
The rendering algorithms are significantly different from the previous versions.
This seems to be a major issue to me, since i have to now test the appearance of my pass with new version. And have to think about optimising the design across all the versions.