I see that the best solution would be if InterSystems would make this package available as an open source, with an option to upgrade any existing instance with the open-source version by using IPM for instance

In this case, any team that keeps using ZEN may provide their thoughts on how the modern ZEN should look in the form of PullRequests. There would be a place to post bugs and feature requests, which some community members may help to solve for everyone.

GZIP format itself does not support files, it's just a compress, usually it can be used with TAR format, which helps to merge multiple files, which can be compressed by GZIP

Look at my project isc-tar, which implements an internal way of creating cross-platform archives without calling external archivers.

https://openexchange.intersystems.com/package/isc-tar