Would welcome knowing if this has been considered or there is reason not to.
This seems backwards to me. The question should be if there
is a reason to switch. Unless DNG 1.4 supports some specific feature that would benefit CHDK users, there is no reason to support it.
I've skimmed over the spec a few previously and haven't seen anything that would obviously offer a big improvement for CHDK. One thing to keep in mind is that most advanced DNG features aren't widely supported, so even ones that would theoretically be useful (like badpixel opcodes) aren't as useful as one would hope.
seeing how surprisingly well DNG 1.4 works on a phone that should not be capable of RAW/DNG, maybe it would work on Canon cameras where DNG 1.3 does not
It's very unlikely this has anything to do with DNG version. The basic format is the same, the newer versions generally add optional features for specific use cases or kinds of hardware. If the images from your phone app work better out of the box than CHDK images, it's because the people who made it had the resources and documentation to make that happen, not because of the DNG version.
