No immediate plans at present. No one has ever paid for a "subscription".
The website simply mentions that if/when never versions exist, they will be provided.
I do always hope to return to Ethereal. But between Torch, and maintaining and extending OpenBench, and now possibly trying to provide a new rating list powered by chesscom hardware, I just don't have the time. The work that would appear in Ethereal, is more broadly seen in the influence that Torch and myself exert over other engines. And frankly, anything I would do with Ethereal, would not be novel. All of my good and original ideas are in Torch, and they very slowly appear in the outside world. I would violate my obligations to chesscom were I to start developing Ethereal in novel ways.
We'll see. The "pathway" to turbo charge Ethereal's elo is quite clear. Ethereal was ahead of the curve when I stopped -- and is not too far behind now, despite missing ideas and code that is considered fundamental in the current era.