I think it is now safe to say that the dts file is OK and that mainline 3.15 or 3.16rc is table on this device. I've been running the ix4-300d for 48h with 3 disks (2RAID0 & 1sata) doing bakcup, rsync, gcc compilation on 3.16rc kernel with no error, or weird message in dmesg or message.
I made a last commit to the github project that includes the nand configuration in the kernel config & dts so nand is also supported.
That is to say that only CESA and HDD led blinking on disk activity are left over (but they are no show stopper to me) so I won't spent any more active time ont these two for now.
So far I've migrate my previous nas to this one and will be running my device as production. so no more experiments on it
... except the lcd driver that I might evolve along with a daemon to display usefull information on it and get user interaction from the select and confirm button, but that's more applicative development than kernel stuff...