I know you don't like "design by committee" and overly complex formats. Also, the compression algorithm itself is somewhat independent of the "container format" that it's used with.
However, if I may make a suggestion: If you do end up rolling your own container format for any reason, always include a way to store the colour space of the image!
Treating RGB images as arrays of bytes without further tags is like treating char* as "text" without specifying the code page. It could be UTF8. Or Latin-1. Or something else. You don't know. Other people don't know. There's often no way to tell.
Similarly with colour spaces: sRGB, Display P3, and Adobe RGB are just close enough to be easily confused, but end up looking subtly wrong if mixed up.
However, if I may make a suggestion: If you do end up rolling your own container format for any reason, always include a way to store the colour space of the image!
Treating RGB images as arrays of bytes without further tags is like treating char* as "text" without specifying the code page. It could be UTF8. Or Latin-1. Or something else. You don't know. Other people don't know. There's often no way to tell.
Similarly with colour spaces: sRGB, Display P3, and Adobe RGB are just close enough to be easily confused, but end up looking subtly wrong if mixed up.