How popular is PHP ZIP extension by hosting providers? Can I use it as default archive software for my WordPress plugin or should I take a look at another lib?
It's probably easiest if you test for the existence of the extension in your scripts, and use your alternative if Ziparchive doesn't exist. I use a wrapper class that checks whether the class is present, and switches to using pclzip (which is included in my library distribution) if not... but all the calls are made to the wrapper to pass on to ZipArchive or PCLZip as appropriate.