It was pretty specifically a Kojima/Del Toro project, so with Kojima having separated himself from Konami... I'd say chances are close to zero. No doubt there will be another Silent Hill one day, but it won't be whatever they'd been putting together before.

There are some conspiracy theories to take a bit of solace in though. Some believe that Kojima's next game, Death Stranding, is pretty much taking up the reigns of his intentions with Silent Hills as it is. So whatever we would have seen in SH (conceptually, at least) may still be making an appearance in that (EDIT: Mr357 beat me to mentioning it).
Still others (myself included) believe that Kojima never actually intended to make Silent Hills a full game to begin with; rather, PT itself was made as a kind of artistic "resignation letter" from him to Konami. There's some really interesting, interpretive proof out there if you look it up.

Besides, I think PT stands pretty well on its own regardless, doesn't it? PT had its own horror gimmick of traversing the same hallways over and over as things slowly change and warp around you; a full game of that would be absolutely ludicrous (not in a good way). And if it wasn't going to be like that anyway, and was going to open up into a more traditional Silent Hill game... then why would PT hype us up for that? It'd be a completely different experience from what the "demo" showed us, and it was the "demo" that made us excited to begin with. So what would even be the point?
PT is pretty much its own game, and can fully be appreciated as such. Pining after a full on "Silent Hills" is kind of meaningless at this point.

Death Stranding might be what you're looking for. Obviously it won't be exactly the same, but there's some fairly strong evidence that it's going to be a spiritual replacement. There's a long video I can dig up if you're curious.

I wouldn't necessarily be opposed to it being improved upon, but like Kiba and I mentioned in another thread, the compressed audio actually contributed pretty well to the atmosphere back when we first played the games. They are, after all, based in the 80s and take place across Asia; the compressed audio mimics the feel of an old 70s/80s karate/kung fu dub.
Much like putting intentional film grain into something to make it feel older, the compressed audio helps to plant you firmly in the 80s. Decompressing the audio wouldn't kill the games or anything, but it would detract a bit from the Shenmue I know and love. As it is, nothing else in gaming really sounds like Shenmue; you can hear an uncredited voice clip from it elsewhere and know immediately that, yes, that's Shenmue. I personally kind of like that it's so identifiable that way, and "improving" the audio would only serve to remove that aspect.