The ability for WW to be portable requires only one thing, an option for WW to use a file rather than the Registry for it’s settings and all the weather.com data.
Ideally the file could be specified to be in a location other than the WW program folder, and so could the html files, but those functions while helpful aren’t required.
Concerns of performance are not as important to people who use USB sticks and can be addressed with the use of RAM drives (especially ImDisk) and virtual disks for those that are.
If WW’s Registry IO routines are modular the change to support a file should be straight forward to make.