[Andreas]

Not supporting hacked boards is one thing, "intentionally" increasing the danger of security leaks is another.

As said, this is a hypothetical worst-case scenario and most likely won't ever happen.
But it is far more dangerous to use an unused bit for custom things then adding a column to a table (the upgrade script would crash with a mySQL-error if a column with this name does already exist when they try to ALTER TABLE) or introducing new variables (this can of course also cause problems, but only if Jelsoft uses the same variable name; Bitfields will be used sooner or later)

Btw: Creating such a "issuperadmin" usergroup permission IMHO would be pretty easy: In init.php check the bit, if it is set also set ismoderator and cancontrolpanel.
In can_administer() check that bit and if it is set return true, no matter what $do is.