MacRuby is currently listed as a Private Framework in Lion. If it stays that way through release, submitting MacRuby applications will require you to bundle MacRuby with your application, or else risk being rejected by Apple at the Mac App Store.
Regarding point 4, is anyone familiar with Xcode 4 and MacRuby? I'm not finding any information on it, and the nightly build doesn't seem to include any Xcode project templates.