just some comments:
- MAME will still support zip even if 7z support is added
- if the chd format is put to version 5, you most likely have to run a chdman -update on all your chds to recompress them to the new format.
- of course I will add support for v5 chds but this will not include the actual update step. You should use chdman for this. I will add an option which will show a warning if you did not convert a found chd.
- cmpro already works rather fine with 7z, while reading 7z archives is internal, writing is done by calling an external 7z executable. Keep in mind that 7z operations are slower, especially if we're talking about solid archives. As soon as I find time and a better 7z sdk, I may include the writing part as well.
Currently I see a new cmpro at end of February, hopefully with the chd update and definetly with the multi softwarelist support.