I am wondering whether we can use our own identifier when passing a document towards box-view and then on the basis of this identifier request a view session. This would prevent us from the need to implement an identifier mapping between the box-view id and our own local id's.
Specifying your own id is not currently possible with the View API. You can suggest features by sending an email with a description of your desired feature to view-api-features@box.com. It helps if you also give some background and use cases for the feature (in this case it's pretty obvious, though). I'll go ahead and suggest this one on your behalf.