There are two versions, the second one has a Raspberry Pi 0 as an accelerator; I'm not quite sure how that works does that suffice for your needs?
I'm kind of close to this project.
There's two things:
1. Pi0 is not powerful enough to run a decent OS (say lubuntu, for example) and let's not even talk about starting a LibreOffice instance or a normal web browser.
2.Even if Pi0 was powerful enough, that thing works as just an accelerator for the ZXOS... it does not allow one to start another OS that allows one to do regular work.
It's a terrible shame, if you ask me.
If developers had a bit more vision on their very first release, ZX Next could now be the Pi 400...