Hello Andrew,
That's an outstanding idea! I am your target audience, absolutely. Here are some things I'd find very helpful at such a site.
1. For Bach, for example. Take the WTC fugues. Produce a score that has each voice written separately with fingering indications to show what fingers will be used when the voices are all put back together. With that, one can practice the individual voices with correct fingerings and get it all into your head before trying to put the counterpoint together. I do this myself, but it's slow, and it would be great to have pdfs of such a breakdown available quickly.
2. For Classical sonatas explanations or leading questions to help see why it is built the way it is. My guess is that most pianists who can play a Mozart or Beethoven sonata have some idea about sonata-allegro form, but there may still be questions worth exploring. For example, why does the Beethoven Opus 14/1 E major sonata have a development section largely unrelated to anything in the exposition? In the same section (the A minor bit in the development) you could have technical suggestions on how to play the rapid LH arpeggios, circular motion, and all that.
3. For the Chopin Etudes (not that I or other amateurs are likely to play them that much) you could make simplified outlines or breakdowns so that people get the structure before they tackle all the notes.
4. For many pieces a bit of history on the composer and what is known about the circumstances of the composition of the individual piece could be interesting.
5. Similarly, for many piece, explanations or leading questions about how to think of the piece as a whole, peaks of tension, pacing, that sort of thing.
6. Listing pieces that are canonical examples of specific technical challenges. Or even excerpts of famous pieces that can be used as exercises for specific techniques, the tremolo in the Pathetique, sustained trills from the Waldstein, wide leaps from any number of Scarlatti sonatas. Since these challenges may represent the hardest aspect of a well known piece, using them as exercises may open up the whole piece to people who'd otherwise be afraid to tackle it.
I'll try to think of other possibilities. I think this is a great idea.
Go Yale,
Bill '80 Timothy Dwight