Have this idea about scores and lyrics, what do you think of it?

[Freso]

As a first glance, it seemed like IMSLP was only for scores in the public domain, but then I found this:
http://imslp.org/wiki/IMSLP:Creative_Commons_and_Performance_Restricted_licenses

So it seems the work creator can also publish scores to the site under, for example, Creative Commons licenses. This I what I would suggest to do. To quote Cory Doctorow (who also happens to be a MetaBrainz board member!):

Now, onto the artistic case. It’s the twenty-first century. Copying stuff is never, ever going to get any harder than it is today (or if it does, it’ll be because civilization has collapsed, at which point we’ll have other problems). Hard drives aren’t going to get bulkier, more expensive, or less capacious. Networks won’t get slower or harder to access. If you’re not making art with the intention of having it copied, you’re not really making art for the twenty-first century. There’s something charming about making work you don’t want to be copied, in the same way that it’s nice to go to a Pioneer Village and see the olde-timey blacksmith shoeing a horse at his traditional forge. But it’s hardly, you know, contemporary. I’m a science fiction writer. It’s my job to write about the future (on a good day) or at least the present. Art that’s not supposed to be copied is from the past.

(From the preamble to his novel “Little Brother” (available for free on his website).)

But eh. It’s your decision to make, and people who work on open source, open data projects are unlikely to be completely unbiased on this matter.

If you do end up posting the scores to IMSLP, note that you can link the IMSLP pages to the Work entities in MusicBrainz. (And the same for lyrics, if you post your lyrics to Lyrics Wikia or some of the other white-listed lyrics sites.)