I believe, BTW, that in the last show, we all sort of "assumed" what Magnum knew, ie, Robin Masters was indeed Higgins.
But the they turned the knife a bit to leave us hanging, at least a possibility that he was not.
I think you have a point; there doesn't seem to be much more that could be exploited from the old show, other then a few "twists" on the Higgins-Magnum relationship.
As an aside, I actually have all the shows on DVDs and have really enjoyed it. Like so many series, you can really appreciate how the ensemble started to work together as a team, each falling into their roles and character. A great show for the '80s', and it still entertaining to watch.
Personally, I'd love to see a one-time "mini-movie" that kind of ties it all together, kind of a "30 years later" thing, and then lets it go. I'd watch that!
Another show, actually a precursor to Magnum PI, was ""Tales of the Gold Monkey" 1982-3 I think. It featured a just before WWII ex-Flying Tiger, who flew a Grumman Goose in the South Pacific.
It had a "Indiana Jones" flavor, and actually had a few characters that were featured on Magnum PI.(Marta DuBois-Magnums wife, Jeff MacKay-"Mac", and John Hillerman-Higgins, of course!) I think it was a "one and done" kind of a series with 22 episodes and never went further. Check it out!
Stephen Collins and the jack russell with the eye patch.
The mini-movie idea sounds interesting. Magnum was a SEAL in Viet Nam in-show, and the new show has his daughter apparently in Navy Intelligence. They could tie the thing together by having some operation that Magnum was part of that was “off the books” come back to bite him hard:
His daughter has just been dumped from the Navy due to her own blown operation, and comes home to stay with Dad for a while, and Magnum introduces her to the old gang and even gets back into the detective business for a bit, mostly working cases for the wealthy and powerful on the island, now that he has a younger helper to do all the legwork. Everything is going great, when Magnum’s past resurfaces and kills him. The daughter then discovers that there’s some kind of link between her own op and the one that led to Magnum’s death, which is what draws her into trying to uncover the real story. She still has a few open cases, which she continues to work at, and finds that some of her clients have connections she can leverage to get additional information for her own mystery.
The show writers can either use the mystery of Magnum’s death as the main arc, so that when the show eventually winds down they can have the daughter discover the secret, thus vindicating herself and getting closure on her father’s death, or they can have her resolve that arc in the first season or two, but have it so that solving that mystery reveals a rabbit hole of other criminality involving national-level spy/intelligence agencies so that she always has “big” things to solve, while still working mundane detective cases in Hawaii (which occasionally turn out to have connections to the “big” world she works on herself.
I’d watch that show.