I’m continuing to think about this and what might work for “book queues”. A few tidbits:

• Apparently some library systems allow “active” and “inactive” holds, which might kinda help the problem (i.e., place an “inactive” hold on things you don’t want to read yet).
• An argument for the processing happening inside the library: people on long holds lists. See the comments on this post at Seattlist. This isn’t generally my situation, but I see the problem.