This worries me. Because presumably, changing the compression algorithm will break backwards compatibility, which means we'll start to see "png" files that aren't actually png files.
It'll be like USB-C but for images.
The PNG format is specifically designed to allow software to read the parts they can understand and to leave the parts they cannot. Having an extensible format and electing never to extend it seems pointless.
And considering we already have plenty of more advanced competing lossless formats, I really don't see why "feed a BMP to deflate" needs a new, incompatible spin in 2025.
Other than JXL which still has somewhat spotty support in older software? TIFF comes to mind but AFAIK its size tends to be worse than PNG. Edit: Oh right OpenEXR as well. How widespread is support for that in common end user image viewer software though?
More generally, PNG has a simple feature to specify what's needed. A file consists of a number of chunks, and one bit in the chunk specifies whether that chunk is required for display. All of the extensions I've seen in the past decades set that bit to "optional".
For example, this update includes a chunk containing EXIF data. As you'd expect, the exif chunk sets that bit to "optional".
