Well, as promised, I am following up. I found a semi-private charter option.

For at least the near future, the Four Seasons Lanai Sensei (formerly Koele), is offering free air charter flights to/from Oahu/Lanai with reservations. The flights are on a 8-seater Pilatus PC-12 https://www.lanaiair.com/#aircraft .

According to a friend who did this last week (along with two other couples), the aircraft was very quiet and it was wonderful not to have to go through TSA and the HNL/LNY terminals.

We are seriously thinking of this option as a get-away.