If 1200 motors are available separately it might make some sense to go thru the process. I can't imagine taking a whole new Thruxton R apart, chucking the alloy swing-armed frame and rolling chassis made for that powerplant.
With the hybrid you would end up with a heavier bike that likely wouldnt be on par with the donor R for handling.
But these things don't have to make sense, someone will always try it anyway. Fun to look at!
Many of the original Tritons used cast off Manx frames as the Manx engine was used in car racing. Norton wouldn't sell the engines separately so car racers bought a complete bike and sold off the rolling chassis to Triumph lovers who wanted a bike that handled.
Then there were the early Dommie's and the later Es2 singles. Adding a 650 Triumph engine to those frames did increase performance.
As far as the 650 Bonnie vs 650 Norton SS, no contest, the Norton is faster. Its doubtful that many 650ss bikes got converted to Tritons.
Maybe the most logical modern day Triton is the 1087 AC bike made from an 865. There are 865 engines available from wrecks. The engine mods to go full 1087 hotrod aren't cheap tho - somewhere in the 10-15 k $ bracket .
Then all of the work fitting that engine to the Norton frame and making it all work...
Better to just make the 961 work I think!
Glen