Interesting idea. I'm not familiar w/ the exact fitting (but I've seen sim.) but your post sent me back to look at a furniture hardware catalogue to see if some similar fittings were there. Boy oh boy oh boy ! - they've got all kinds of fun stuff in there!

But back to your idea. Specifically, I can think of only one type of pin that uses a controlled detained ball - the socket wrench. Locking socket wrenches lock the socket with a ball bearing and release it by pushing an internal pin that has a round depression that the ball rolls into thereby releasing the socket. I guess if expense, weight and sand contamintion were no object, maybe one could do this - Yeah right!. But there will be others - but I think ball detents and their locking mechanisms are complex. And you would need a different arm to release each pin. And all those little buttons would be visib le.

Stepping back, what you really have is a mortise and a tenon - with the tenon being variable. Well, there are bunches of these! Mostly visible, though. The simplest being just a screw bolt from the hatch into "t" nuts (etc.) in the flange....

An invisible variation:

Aligned hidden pins pointing down from the hatch (say 3 ea side), pins large enough (say 3/8"d) for holes or slots cut in the end. Holes thru the flange and (hatch or flange) gasket so that the pins protrude into the volume below. A guideway from the cockpit to the pins to guide a rod thru the pins. Or a guide way for a moveable channel if slotted pins. To remove hatch, just pull the rod on ea side.

Anyway, I guess there are lots of ways, but what about some of the other stuff I saw in the catalog? What about cabinet height and sideways adusters used to attach the forms? One knobs adjusts vertical and the other for horizontal. Adjustment about 1/2" ( I think). At about $3 ea., it might be worth it for some.

Also what about the hardware for knock down furniture? Sand infiltration and corrosion aside, the cam locking system and captured end fittings could easily(sorry, I get carried away) be modified for another type of hidden hatch latching system.

However, I would be really interested to hear what you've come up with. Let us know your progress even if you've rejected the idea.