To start with let us look at some observations :
1) Korg have been moving away from using third parties like Yamaha and Fatar to supply their keybeds, and making their own. New products (M3 & M50) all use the new keybeds I believe and so will any other new pieces coming out of the factory presumably. The original Oasys 76 uses a Yamaha keybed. The 88 uses a Korg RH-3 IIRC.
2) When the M3 was released the 73 key version was delayed, and the same is going to be true of the M50. I assume that more 61 and 88 keybeds are made initially, and those take priority because they are the most popular. So the 73 is associated with manufacturing delays or deferrals.
3) Korg often release OS 2.0 updates that bring a raft of new functionality and that update is used to 'relaunch' an existing product. This happened with the Triton, the Karma, the Radias, the M3 (especially!) and from what I understand many of the arranger products. That appears to be one of their strategies, and a very sensible one too.
None of the above observations are too wildly speculative

So maybe the reason for the O76 seemingly disappearing and the reason for the slightly longer than normal silence with regards to Oasys updates is the following :
Korg are going to 'relaunch' the Oasys with a significant OS 2.0 update and the Oasys 76 is being replaced by an Oasys 73. The 73 keybed manufacturing has interrupted the flow of Oasys hardware and the software is taking it's time because it's a big update !
See how that scenario could be what is happening here ?
In my mind that is a reasonable interpretation of events, and possibly more reasonable than speculating that the Oasys is being totally discontinued.
Time will tell ... but the time for gloom is not yet here

Daz.