Anil Roychoudhry has announced that he has been working on a solution for USB keys within ICA sessions.
Please read about it here.
Already there has been a high degree of interest and I would expect that Anil will be considering making it more publicly available. His blog site is listed in the blog roll on the right.
The ability to allow for dynamic USB key insertion/extraction into an ICA session is something that people have been asking for. USB keys are now the defacto standard for transferring data between computers not connected through a network.
Please do not expect a full solution since this is only a prototype to prove the concept. I would predict that interest might trigger a future project to include this with Presentation Server.