As far as the 2 stroke big bang NSR500 goes. Honda had thought about doing this for years, and as it now appears the RC30 was using a big bang type config.
It wasn't really Doohan that used it, both he and Gardner used it in 92 and it was no doubt tested to death by guys like Beattie and Itoh who were running in the Japanese 500 (yes can you believe it there was a national 500 series then) series at the tail end of 91 and early 92.
Doohan didn't like it initially until he saw his laptimes! And he dominated 92 until his crash, When he came back in 93 the bike had been engineered again towards Gardner who was a throttle jockey who rode hard but was not the same type of rider and only ever wanted power not balance. And in 93 HRC wanted to use an electronic carburettor too (it was never true fuel injection). They used it in the first race and Doohan and Beattie told them they wouldn't ride again if they were forced to use PGM Fi again! So it was only on Itoh's bike from then on and did the magic 200mph at Hockenheim later that year (though HRC tried to tell us they hadn't)
And he didn't like it later on in his career when guys like Okada, Nobu Aoki and particularly Criville could look at his data and see what he was doing and use it to go as quick and push him and sometimes though rarely beat him.
So in 1997 he asked Honda to build a 180 version that was not Big Bang, just like the 89 engine he had that almost killed him in his debut year!
He did it for no other reason than to psych his opponents, and also to try and recover the close throttleconnection feeling he lad lost with the big bang engine.
What he found was fairly amazing, the electronics had moved on so much, he got BETTER tyre wear with this engine and linked to unleaded fuel that took the edge off the power delivery as he was able to modulate the throttle much, much better. And he dominated again.
Criville and Okada both binned it the first time they tested it!