Assuming there is some legal framework allowing a smaller entity to piggy back on Mozilla or the Linux Foundation's non profit registration in the developer's country, the dev still needs to at least register as an official entity, which can be awkward depending on their status (do student visa residents get a right to do that for instance ?). There's also the more complex cases of a for profit business publishing an open-source app. Do they need to register a different non profit entity to avoid paying for the open source part then ?
To then explain to Apple how the arrangement is made and have them approve it is another story as well, as we're already seeing that Apple has no intention to make things simple regarding any of these rules.
All in all, there will be clear cut cases that will show it can be simple, but I totally see a long tail of devs stopped at any point of the process, and it's probably by design.