I think you miss the point about the twin turbo, polished con rods, tricked-up ECU's on a 1200, Robbie boy.
They are done for only one reason.... Because they can be done, most usually as nothing more than an advertising hook for a company's other engineering services. A bait that seems to have at least attracted some open mouths.
Nobody with half a brain is going to build one or (more likely) pay to have one built to use on the road for a protracted period of time. But as a one-off, sprint fun in some bizarre class or other, or just to stand at the Motorcycle Show in Brum or Little Rock, AK for bods to gawp at, slack jawed in wonder, it's quite OK. Now relax and work out how to get that extra 10cc of oil into your topbox before you go to Tesco and buy soft fruits.... Or devote even more time to worrying about the potential faults with YOUR bike, which you now apparently regret buying.