You can clear coat anything, i don't think that tank is too highly polished, what they do is get the alloy blemish free and really clean and then clear coat it. A lot of that shine is brought out by the clear, the tank doesn't have to be that shiny too look shiny, its the clear that creates the shine. I have repaired a clear coated surfaces that were worn by lightly sanding it, this makes it look very cloudy but when the new clear coat is applied it brings the transparency and shine back. It can definitely be done. You would have to look at something like polyurethane UV rated clears, like they use on some boats, there are even some good epoxy 2 part clears that are very good. I work with industrial clear coats and epoxy products, if you look around you will find something that will do the job. I have also seen highly polished mag wheels {on an old GSXR} that had been clear coated and looked great although i don't know how long the finish lasted....
I plan on looking further into this on one of my projects but it will be a way off yet....