More seriously, though, I would expect that being able to impose restrictions that can't be circumvented by any intelligence no matter how super- is the real hard part, while coming up with reasonable constraints is comparatively easy (although perhaps not trivial).
From such a POV, the danger would lie in intelligences that are powerful enough to be dangerous but not smart enough to defeat themselves, or from external malicious use of obedient AIs. Once they get smart enough to circumvent any restriction humans put on them, it would at least become obvious (with fair warning ahead of time due to the relatively benign wireheading failure mode) that caution is needed.
We're far from there yet, and simple recursive self-improvement can't get us there alone, because wireheading looks like a perfectly reasonable solution to a simple recursive self-improving process, absent external intervention by human capitalists.