I'd almost argue it's easier to form a non-profit entity that become sponsored by a non-profit organization such as TLF.
This almost reinforces the parent's point.
If you are expecting less than $25k in revenue (donations, grants, program service revenue, etc.) in each of your first three years, you can use the IRS's abbreviated process and get setup within a month (for the cost of setting up a corporation with your state government). If that exemption doesn't apply, it can take the IRS over a year to approve your application for tax exempt status. There are also significant compliance costs that can be burdensome for a small organization.
The TLF is a big dog for big dog projects, and I was just using them as an example of the structure. The Apache Foundation has their own flavor of governance, as does Numfocus (which sponsors a bunch of scientific computing projects). I'd expect that this move will probably trigger the creation of some "mobile app developer collective" organizations that specialize in this kind of thing, kind of like a "digital makerspace".
Could one sign over stewardship to the FSF? They're non-profit I think.
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.
If you like to have an organizationalnumber, you need to apply to the tax authority. If you do business activity and like a local name protection you need to apply to bolagsverket. Depending on the size of the app these steps might be helpful. I don't think our local chapter of FSF, has done any of the registrations just as an example. They run local conferences and other simular works.