I'm pretty sure Rabaul could have hosted Japanese carriers. My suspicion is that the presence of American 4-engined bombers based at Port Moresby may have dissuaded the Japanese from ever basing their precious remaining carriers there. While the B-17s and B-24s were pretty lousy at bombing moving carriers they could probably be expected to be lucky enough to occasionally pummel anchored ones.
In a bizarre postscript to this behavior after the war, the Japanese government also recruited 55,000 Japanese women for the "Recreation and Amusement Association" following the surrender. These women were expected to form a "sexual dam" to protect the majority of Japanese womanhood from the appetites of their occupiers. There is evidence many of these women were recruited by coercion. It is unclear how much the U.S. occupation authorities knew about the program, but in March 1946 the RAA brothels were declared off-limits to U.S. personnel.

I agree, no doubt had the Japanese took Moresby and held GC, they would've used it as a base for carriers. Most I read on it was easier to supply and protect the large assets at Truk. Rabaul didn't see air attacks until 43.

It was certainly smart to leave it rotting on the vine, wisdom they failed to use in other areas during the Island hopping, but hindsight is 20/20

Charming.

Why do I never find these mine fields...