Not the end of good news guys
I cut into pieces RK_MLC_USBFS_SD.A this lib and elicited only those functions that are necessary to access SDCard. It reduced the code size and memory dramatically. Also I am thinking that maybe we can do the same with flash memory driver. I didn't succeed with flash because there was too much of the code to put into the memory so it always kept hanging, but perhaps it will work if I remove all the unnecessary functions from this lib and leave only I/O low level access to nand flash. Two versions may be needed though (SLC and MLC).
If it will work, it's great! Not only because of the full access to the files, but also it will be possible to make a backup of the firmware using RKP app.