Can not compress to zipx
Why would you want to? It's not compatible with Zip, and if you don't need compatibility there are better archive formats like 7z.
The archives plugin can extract some ZipX files (any that 7-Zip can handle) but we've never seen the point in letting people create them, and I don't think anyone has ever asked for it before.
It does not have to be it is an advanced version of zip that has more compression and in some cases is better than 7zip. You have support for it in powerarchiver and peazip which is essentially a file manager with better compression formats. By not adding formats like this you are turning away people who need advanced compressioin and archiving.
ZipX is a proprietary version of Zip that's incompatible with most programs that understand Zip files.
Even things like 7-Zip only support a subset of the ZipX compression algorithms, which aren't all available for other projects to use as far as I am aware. (My knowledge may be a little out of date as I haven't had any reason to look at ZipX in many years, but AFAIK it hasn't changed.)
Opus can decompress the ZipX files that 7-Zip understands, but won't create such files.
If you really want to create ZipX from Opus, you always have the option of making buttons or context menu items which create them using other archivers. But I would urge the use of more standard archive formats, especially if it's data you may need to access a long time in the future. ZipX has not taken off and was more or less DOA the moment it came out due to it being proprietary and not being better than other formats (or not for long, at least).
Also, PeaZip only has partial ZipX support, the same as 7z (source):
custom WavPack, MP3 and JPEG pre-compression filters are currently unsupported (both for reading and for writing).
(You can add a closed-source plugin to get WavPack support, but not the others.)
Apparently PowerArchiver does support more ZipX algorithms (source):
jpeg – Codec added by WinZip for specific support of jpeg images. PowerArchiver is only archiver currently that can extract zipx files with jpeg codec.
I'm surprised they claim to be the only archiver, unless WinZip no longer exists or dropped support for its own format. But they're about the only one.
The ZipX format came out in 2009 and is already dead. It seems only two programs in the world fully support it.
I disagree with that assumption. I use zipx all the time and in some cases it is better than 7zip. Its down to personal choice. You support cbz, cb7, cbr but that is not widely used .
They're just standard zip files with a different extension.
yes but why have them? you don't even have cab compression cause you say these formats are not widely used well they are. Wide range of support for archive types would bring people who use dedicated archivers to Opus. File managers need to embrace Archive types to attract people who have to decide dedicated archiver or a file manager like opus. Thought archiving was file management or am I missing something.
Couple years ago I played with zipx. There are only 1 freeware totally which support zipx jpeg & wav decompresssion. It is BandiZip. More correctly it is an adware bu you have WinZip but your friend doesn't have it it would be only one reliable option or you can create a self-extracted archive. All of other software which decompres jpeg and wav in zipx archives are commercials.
Powerarchiver supports zipx. my point was that Dopus should support a wide range of formats to make it universal where they are widely used or not. Then people can have a wider choice. By limiting to just the standard archive formats you get some people questioning is it worth having a file manager or archiver as they do basically the same thing.
Opus already has partial support for unpacking ZipX, about as good as most other options.