Here is my request. Well, I already know there are some documents (tutorials, manuals, guides etc.) to do that... But it would be really great if we had this feature by default. For devices like x86, RPi...
Wishing you Merry Christmas and happy new year in advance,
I would say that this level of automation (expand the root fs without asking anything at all) is a bit too much. One-button expand to the maximum available size - I would support this. Auto-expand - no. And here is a reason.
There is already some code that attempts to preserve custom extra partitions during the sysupgrade. This way, now one can install OpenWrt on x86_64, think a bit, create a third partition, format it as ext4, mount it, and serve it via SAMBA. And the contents of this partition would persist during the sysupgrade.
In other words, extra partitions seem to be an already-supported and important use case that should not be broken. Without the extra partition or a separate disk, one cannot preserve these shared files across a sysupgrade, unless they also fit in the RAM.
By implementing unconditional auto-expansion, the possibility to add an extra partition would be greatly diminished, because it then must be created outside or OpenWrt, before the first boot. Not all operating systems have convenient tools to create partitions on arbitrary storage devices, so the use case above will be hampered.