I have thought about this alot, and done alot of offline testing. First, CCW only for me! No OC because it might frighten civilians lol.
So for a more ADV type bike it would be a holster located inside the tank fairing. Even my crf300l rally has room for a 1911 (which is the smallest possible useful tool). This would be perfect for unobstructed QD while moving, or at a traffic signal in Portland (not that I ever go to Portland). If it rains, just put a baggie over the pistol, punch a hole for the trigger finger. In fact use a black plastic bag, since that will keep the gun concealed when moving it to the shoulder holster for enterring starbucks etc.
But the more I think about it, I really can't see going pretty much anywhere without the AR and some grenades, so guess I'll sell the bike.