If Honda used the RC51 engine in another bike like as asphalt adventure bike I'd be first in line to purchase it.
They did Jimmy, the XLV1000 Varadero. It's based on the VTR1000F road bike, the Poor Man's RC51. The RC51 was the hard nosed racer that wiped the floor with Ducati V twins, (that only won races because of the 33% capacity increase they were allowed over Japanese inline fours) whereas the VTR1000F "Firestorm" was the softer, more comfortable road version.
It wasn't as powerful as the SP1 (or SP2) and the one "Achilles Heel" is that Honda cheaped out and replaced the SP1's gear driven cams with chains, and of course, the factory cam chain tensioners are prone to failing, so there are lots of reasonably low mileage VTR1000's with damaged valves, but once fitted with a set of APE's manual tensioners, they are pretty much bullet proof, and much easier to live with than anything from Ducati.
I bought a VTR1000F cheap because of the cam chain issue, and while I loved the engine, the handling, etc, the riding position doesn't suit, in fact I think it's more "racer oriented" than my VFR750.
I found a crashed 2006 model VTR1000 and am in the process of turning it into a more comfortable "Daily Rider". I've fitted superbike bars and am in the process of lowering the footpegs an inch or two, and I think it'll be a great bike to ride, all the benefits of that great V twin engine, with powerful brakes and excellent handling, without having to ride like the Hunchback of Notre Dame. I sold my standard VTR1000 to a mate, who loves it.
The Varadero isn't the prettiest bike around, but would be a great adventure bike, especially with that big V twin (well, it's an "L" twin actually) and if you want more power, an RC51 engine would probably bolt right in! Cheers, Terry.