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Starting with >>23.05.5, 16/128 will be the lower limit. Given the pending release of 23.05.0 within the next few weeks/ months, it does make sense to use those as lower system requirements in most places (there is a lot of content and touching it once helps keeping it current for longer).
Wow, I personally consider 8MB of flash to already be "drum-tight" for space. Call me soft, but I consider a web-gui to be a must, not a frivolity. It's helped me understand like a dozen convenient new ways to use the router, just by how nicely all the menus and features are invitingly laid out.
Those "efficiency demons" who can suffice with 4MB of flash on their really-cheap, rather old routers, maybe should have a "4" that's blazing on fire, in the hardware database (one step even more dire a warning, beyond a "red 8"). The burning flames around the 4 mean "for efficiency demons only".
After making-do on a router with only 8MB of flash, and experiencing how easy it is to run out of disk space (and the subsequent tricky recovery - including a factory restore, and restoration of a saved firmware backup config file), I agree that it's only at 16MB of flash where any comfort and decency of straightforwardness in administration begins, to speak of (so that new users don't run out of space immediately after that first heady - nay, thrilling - software package installation - all-too-quickly setting a sour taste in their mouths for the OpenWRT experience). FWIW, I feel this is the right minimum flash size to warn users about having, going forward.
BTW: it's too bad a new package install wasn't, by default, done first in a "dry-run" sort of way in the tmpfs first (using opkg's "-d" option), to see what all the total sizes would be after full decompression, including dependency installation (and then undo it again, after total size calculation). This is granted there is enough RAM, which I feel is safe to assume is much more plentiful than flash space. Then if the flash still has enough space, immediately do a non-dry-run install.
I say this because today I installed a software package that claimed it was only 5KB in the GUI, but after installation (along with all dependencies) this ballooned to actually taking more like 700KB, devouring about 70% of my available, precious 1.2MB of free flash space in the overlayfs (after fresh installation).