GregS,
There is no specific mechanism in epub to use your WUID, but there are several optional metadata fields that might be used for such a thing. However, any use of such a data field would have to be taken care of by custom software. Standard epub readers wouldn't know what to do with it.
The ability to select different stylesheets may be problematic, also. I see nothing in the epub spec that addresses this. In fact, I was trying to figure out a way to allow a user to switch stylesheets in an epub myself. You can't do it as you would in Firefox, as there is no defined standard mechanism for this in epub. The obvious method of providing two identical copies of the content, but with different linked stylesheets and then selecting the one you want via a hyperlink would work, but would be rather wasteful. Of course, if you use the Firefox Lector plugin for reading the epub, switching stylesheets is not a problem. I'll have to ponder this more. Any ideas?
For textbooks and such, the epub spec certainly could use some improvement. However, it is a new spec and what has been done so far is a very good effort by all involved. I'm sure that future versions will add new capabilities. I just hope that those creating the specs are keeping an eye out on forums like this one.
I applaud your efforts to provide textbooks and related material in electronic form. If only the major publishers would do more of this. BTW, I looked at one of your online PDFs - it is a good thing that younger people have good eyesight. I wouldn't want to read too many documents formatted that way
Look for a PM. I want to ask you about something related to all of this.