iPhone is stuck in Recovery Mode with full storage
I have an idea.

get off the nand flash from the mainboard.
copy all nand flash data to a large one.
solder the large nand flash with data to the mainboard.
update new IOS with itunes.

Because changing a new larger nand flash in China is a very common thing. And there is a nand data mirroring tech in 2016 on Iphone 5C.
So I think Combine these two technologies may be can solved this problem.