Steelsen,

Maybe related but not quite what you're describing: we're developing a requests application that will interface with a number of different systems, including Illiad, Symphony, and LAS, for fulfilling the requests. Specifically, we are:

- adding a Scan & Deliver option for a subset of our materials, for qualified users
- providing a single request process for off-campus materials, regardless of where the material is located (currently the user must use vastly different procedures depending on which offsite location the materials are stored at - and a single archive may have materials in 2 or more different locations)

It's not a shopping cart model, and specifically doesn't solve the problem of enforcing Special Collections request limits across multiple archives. (In reality, for us, those limits are a little mushy, and all requests with limits are mediated - that is, it's up to the division's public service manager to decide whether an extra box will fit on the truck on Wednesday.)

But in case it's useful, here's the current UI design spec: 
https://stanford.box.com/s/vqiy70jdh8jqmgg3s39e6ivk717rfln2

Feel free to contact me with any questions.

Jennifer Vine
User Experience Designer
Digital Library Systems & Services
Stanford University Libraries