"rain bending" already exists. Watch the ATLA series again. Platinum bending is unlikely because the material is so well refined it's insanely difficult to mess with, if at all. Purple fire is literally just fire. Sound bending is just something you pulled out of the wiki that fans have been speculating for years with no confirmation from Avatar Studios. There is no 2025 show. If you're thinking about the Genji project that is confirmed to be a fan-made comic and the studio not even touching it.

no new avatar is coming. a older version of gaang will take place.