It's more that if I break it, I can't afford to replace it. And if it were a real piano I'd feel even more so that way (since a good baby grand can cost more than many cars). There's a certain finish and refinement to them that is very easily ruined if you don't really know what you're doing. If I had access to a digital piano to practice on, I'd probably feel better about modding mine. On the flip side, part of the point of the computer is to be mobile, and while it'd be nice to have one built in to the instrument, it wouldn't be mobile.
Maybe one thing I could do is mount it on the back of the piano to keep it out of the way, although it might be metal back there. And I don't know what's behind it.
Still, there's space down at the bottom (when I get a worklog going you'll see what I'm talking about) where a case could go.