Multivolumes will always be very important. We are going to have computers with 16-gig memory and disks with 25gig content and more. For reasons of time and even safety we may later want to split very big archives, just as we split the content for floppies that started multi-volumes.
it could be useful, yes...
but it is really needed?
I don't think so, a better and more efficient GUI that add more productivity and conviviality is more important if you want a growing user-base .
multivolume could be added later.
It seems to me that the 7-zip project is more about creating a better compression format (7z) than making a better gui, if you want a better gui you should use one of the programs that use 7-zips 7z format and another gui.
7z could have the easiest, most powerful GUI in the world, but would still just be another bit player unless the 7z format is good enough to command respect; the 7z libraries *are* gaining that respect, and being integrated to support 7z format in other products. 7z's compression is already excellent (better than ZIP or RAR) but without the many extra features Rar brings with it, such as multivolume and error recovery.
PAR2 solves a lot of problems with error recovery - but if fully integrated into the 7z product, would give a "one stop shop" to repair and unzip your 7z archive.
adding features puts on the table the problem of back-compatibility and if not implemeted with care also problems when implementing the next new feature.
once multivolume and data recovery are added horganically, I will start complaining about the gui.
I disagree - Drag and drop is a nice option for people who like using the mouse to work with an archive as a "virtual folder" but at the extreme edge there you have products like ZipMagic which extend Explorer to support zipfiles as just a part of the file system (I believe XP has some similar functionality natively now)
Multivolume however relates directly to such things as data redundancy, split storage (for example, storing 10gb of archive on 'n' 4.3gb DVDs or 700MB Cds) and compression efficiency.