Yeah, been watching this carefully as I have over 120 cars/engines with Sergents. Long story short is that Frank changed interest directions awhile back and has been wanting out of the hobby business, even offering his designs and initially the equipment for free. He stopped making the specialized sand-cast couplers, but kept the basic HO type E's in production, which were nicely die-cast, while waiting for someone to pick up the line.
The only serious contender came from China, Inventive Model Works, a smaller firm that makes models and parts including brass investment castings. Eric Xing reversed engineered the Sergent (what Frank was wanting to happen) and produced a run of jewel-like preassembled versions. His intent was to investment cast the unique stuff while Frank or Frank's replacement made the bulk quantity conventional couplers. They sold out quickly, but Eric put it on pause while he finds a better way to ship them from China as Speedpak is unreliable and has no tracking ability.
The big mystery is what is going on with Frank and his diecast equipment. There are a couple of individuals who are interested in keeping that part going (to the benefit of all), but there appears to be unknown issues going on there. And of course, Frank went on deep radio silence awhile back.
Most likely all this is going to work out eventually, and progress is being tracked on both the Inventive Model Works and the Sergent Engineering Facebook groups (the only real use for Facebook).