Congratulations Feldmahler on a job well done - a pity we didn't get to see some more of the really special stuff that is not easily found elsewhere, and thus uniquely IMSLP...
(I'd also suggest having some water to hand the next time you give this talk, it sounded as though your voice was getting quite tired towards the end.)
Rather than the discursive trip into the public domain and copyright I would have liked one particular point teased out for the educators, and that is the dramatic lowering of the cost of entry for study purposes. Say a senior music history class is making a study of one of the Beethoven symphonies; it's rare to find a school or uni library with say a class set (25 copies) of the Pastoral symphony, no. 6. Probably there would be about 5 or 10 copies being shared one between four or five. Not so with IMSLP; everyone can download a copy to their laptop or home PC, though paper copies are still somewhat indispensable in terms of convenience and portability.
I did especially like your comment about "attacking the public domain" being equivalent to stealing books from kids - good to hear some of the positive audience reaction here and elsewhere!
The economics of music publishing of the traditional paper kind make certain types of musical score relatively expensive, full scores especially - which is why you see numerous music textbooks which comprise a whole volume or two just of sources alone, e.g. the Norton scores, which after rushing through most of the common era (prior to 1700!) includes in the remainder of volume 1 major snippets of Vivaldi, Handel, Bach, Haydn, Mozart, and Beethoven, before handling a mixed bag of the 19th and 20th centuries in volume 2.
The same thing goes for performance parts of ensemble works - these are sometimes quite expensive as the logistics usually involves small-ish print runs of numerous fiddly items, so the investment required to purchase a full set is probably doubtful for a range of schools with small musical resources; the IMSLP parts project will no doubt allow a number of ensembles to be more adventurous in their repertoire choices, because the risk of spending a lot of money on something that doesn't turn out to be usable is much reduced.