Spelmusik.net have had an interview with Akira Yamaoka about his music. In that interview they bring up Silent Hill 5 and ask him about the music, here's what he said to say:
"You did about 200 footstep sounds for Silent Hill 2. How many will there be in Silent Hill 5?
- That's a very clever strategy to get some information out of Silent Hill 5! To camouflage the question: the next-generation hardware is pretty sophisticated so you only need like one or two footstep sounds!
Speaking of Silent Hill 5, can you tell us anything about how the music in the game will sound?
- Can I ask you a question first: have we announced Silent Hill 5 yet?
Yamaoka laughes and then we get kind of an answer:
- It is still so far ahead so I have nothing in mind!"
Judging by his last comment it looks like its very far behind, but definatly on the way.