I'm not opposed to LibGD as an extension. We already have several extensions for doing format-agnostic reads.
That said, we already have a perfectly good loader for PNG, and I believe we just store image data in the engine as ZLIB'd bytes. We decompress them at load time, which, unsurprisingly, gives exactly the format that WM extension wants for its icon data. It doesn't make sense to contact this person about relicensing 90 lines of code that ENIGMA already has the exact equivalent of, with the operative difference being two libPNG calls instead of libGD calls.