I don't agree he should go, after all, he's won a race and had podiums !....however I think ditching JB is a BIG mistake. Rossi is still a huge draw and still a great racer, if not quite up with the top 3.
I had a 270 rev 3 was 55 at the time, never had a problem, (but I am quite tall) I found it best to ease it just over TDC let the kickstart up to 10 O'clockish then give it a steady firm push NOT a sharp kick....but if you are resorting to engine mods you have probably tried all this!
rode a 300 (2012) with s3 FWW as only conversion...rode really lovely and smooth, but I find you need to feather the clutch on the bigger bikes to control the "sharpness"
NOT proven until they are penalised for stopping and sections are laid out to suit the rules...all I can say having watched some video (only), enjoyed watching no stop more ( so far)