I have seen it done on the sly while working for a company who had an oven to do it. However it was a classic car and I'm sure the exhaust has a much easier life than on a bike.
Not totally familiar with the process as I can't remember exactly what temp it is baked on. I do know it's much higher compared to powder coating. (could be round 800C but I need to look it up.
The self cleaning ovens go to 450C (800F or so) to burn the crap off, the enamel survives that no problem.
From what I understand it is one of the things that matters as the further away (lower) the working temp for the part is the more resilient the coating will be.
Also how good does resist staining? I have seen it on stove or ovens when they are really hot and something gets splashed on the enamel stains.
Can the chap who does it give you some more info regarding the temperatures involved?
The quality of the enamel varies also as the above mentioned company tried to cut cost by swapping from a german product to a cheaper alternative and the result was as predictable.

Just throwing this out there but exhaust paint comes in white and black, (and probably a few other colors), and will deal well with the heat. If and when it starts looking bad, lightly sand and apply a new coat...
Easier than removing the enamelling if if goes bad at the head. I've seen my pipes glowing on cold nights, what temperature is that? Will the enamelling hold up?