With the ar71xx branch being SOURCE CODE only now is anyone actively working to port the Mikrotik devices to the ath79 branch?
Some NAND support at https://github.com/openwrt/openwrt/pull/2184 (basic NAND framework, upstream SPI-NAND drivers).
I'm guessing the Mikrotik boards use "RAW" NAND, which I haven't looked at in any detail.
There has been progress
Have a look at this new PR