I'm not so keen on changing the defaults. These combinations or some variation of them are usually associated with something else:
H - hide app, window
X - close, exit, cut
But that's why you can change them to your liking.
FYI: I picked them for a reason: Cmd+Shift+Y wasn't used yet, so it made sense at that time. And U for strikethrUUUUUUUU. Also Cmd+U is used for underline, thus if you use shift, you basically lift the line to the middle.
