RIFF is so trivial and has such useful properties that I've done several application-specific binary formats that are RIFF with a different start atom.
A 'RIFF' chunk containing formtype 'WEBP' and a mandatory 'VP8 ' or 'VP8L' chunk, and optional 'VP8X', 'ICCP','ANIM', 'ANMF', 'EXIF', 'XMP ' chunks and possibly some unknown chunks, where if any of these optional chunks appear 'VP8X' must be first, and with certain ordering restrictions on the chunks.
It is true that earlier spec versions only allowed the core 'VP8 ' or 'VP8L' chunk, and the spec does warn that some older software might not support files with the newer chunks, so they should only be used if really needed for best compatibility.