Thank you for taking over maintaining of fuseiso!
I would suggest to add support for ISZ images, which are nothing else but compressed iso.
ISZ is an open file format developed by Ezbsystems for its UltraISO software, here you can find the specifications: http://www.ezbsystems.com/isz/iszspec.txt
According to me is very handy since you can store iso images on your hard disk without wasting too much space. For example if you use databases, encyclopedias etc that resides on CD you wouldn't have to bring with you the cds all the time, but also wouldn't have to waste too much space on your hard drive!
Of course you can compress those images with, say, 7z, but then you will have to unzip them every time before being able to access the ISO image and its contents. With ISZ instead the decopression is on the fly!
ISZ is currently supported among otherss by DaemonTools in windows, but as far as I know there isn't any program that does support it in linux.
Thank you.