True. Industry entrenchment would be a big issue. I can think of two ways to try to fight it. The less viable option would be trying for PSD support, which would be a lot of work. The other option would be to write a Photoshop plugin to allow working with the new file format in Photoshop. This might be annoying to end users having to deal with the format, but also easier developer-wise because you could make sure Photoshop handles rendering right; you’d just need a way to warn about operations in Photoshop that can’t be converted to the new FOSS program’s native format.