"Code folding" would be a very nice feature to have, especially in the package body editor. I don't know if you've looked at SQL Developer (Oracle's free DB maintenance tool), but it incorporates folding pretty nicely.
Looks like this was somewhat implemented in EA 720.1640, but not as well as I would have liked. My reference to SQL developer was to automatic folding based on Functions and Procedures and having "+" and "-" next to the folded code for expanding and collapsing, rather than manually selecting and right-clicking to do it.
I agree that it would be nice. The new editor component we introduce in the next feature release provides some of the plumbing needed, but it still requires parsers for every SQL dialect we support, e.g. PL/SQL, T-SQL, etc.
We have a ticket open for this so we can track how many requests we get for it. Given the amount of work involved, we would not consider this unless we see a lot of interest in this feature. Until then, the "fold selection" feature is at least a step in this direction.