Just catching on to this thread. Not sure if you caught my posting here (
http://chdk.setepontos.com/index.php/topic,4479.0.html) but I had implemented the set_capture_mode_type on my SX10, and tested various modes based on what I had found previously in the firmware to find several working modes that were not part of the regular available modes.
These fell into 4 categories:
1) Named modes that are part of normal camera operation (ie, ones on the mode dial)
2) Named modes that are not part of the camera operation, but work as advertised on cameras they are available on (e.g., fast shutter, slow shutter, digital zoom, etc.)
3) Named modes that do nothing (e.g. ISO6400, Creative Light Effects)
4) Unnamed modes that do something, but I never really tested fully to figure out what (e.g., there were additional mode numbers that did colour swap and colour accent, some that did an extended shutter speed by default, etc.)
On top of this, setting to some modes between the working (or at least settable) modes, would lock up the camera (I didn't fully test the extent of working/non working modes).
One of the interesting things I also found was that I could set custom to one of the inaccessable modes (I currently have it set on Digital Macro which is normally available on the SX10).
This may be of some help in the development here. From what I've seen, it would seem that (all?) modes are (may be?) present and settable in all cameras (at least of the same OS type) just not enabled or fully functional, and that perhaps all cameras (of the same OS) share the mode numbers.
One really curious outcome is the presence of the ISO6400 mode. It doesn't do anything notable, but the only record I have seen of it elsewhere is as a mode available on certain DSLRs. I'm wondering whether this may indicate the the DSLRs share a lot of software portions with the P&S cameras which may be positive news toward DSLR CHDK development.