The i-op system from the factory is a QNX based system. So the answer to your question would be "yes".
Depending on the version of i-op and what code updates it got from netpliance servers, the boot phase of the unit can be interrupted such that a QNX shell prompt can be obtained. What you can then do with QNX is open to your skills.
Another option, which may be what you meant, is to hack the i-op to boot from other means (IDE drive, etc.), but make the alternate OS a fresh installation of QNX. With this approach, you would have full control of the OS, and its boot-time behavior, and overall application.
QNX is a perfectly fine product. There are lots of working systems out there, mainly in the "embedded systems" product space. You could certainly do a bunch of cool stuff with QNX on top of the i-op platform.
The question is, what do you want to do, and is QNX on the i-op the best choice?! QNX is not intended as a be-all general purpose OS. As such, you will not find much in the way of "off the shelf" software to run on top of QNX. But, if you've got a custom software idea in mind, it may be just the ticket!
But certainly not any MS Windows... ;=)