I got my fingers on a software-bricked NAS540, managed to get it back to operating state with the original firmware - and get thinking of...
It announces itself on the serial console as Mindspeed C2000, with 256 MB Flash, 1G Ram, dual 1gig ethernet, three USB3-Ports - but it has a NXP LS1024A dual-core 1,2 GHz-CPU, which I can't find in the 5.4 kernel tree. There exisit an OMV-Port for it based on a 3.2 kernel, the original zyxel firmware is based on a 3.2.54 one. NXP sells a SDK based on OpenWRT for it - for 25.000$ p. a., dunno how outdated their kernel resources are due to the price tag... There is an attempt to port the 5.x kernel tree to that CPU on github, so it isn't completely hopeless to get it working. But maybe for me, I can't program, only some shell programming... But I have a testbed and am willing to mess around with it, I have in that state no use of it... The NAS520 and the NAS542 have the same boards in it according to some internet research, so it'd cover thrree devices if that info is correct. Is somebody interested in porting OpenWRT to that hardware besides me? With skills that'd probably lead to success?
I really don't have any layerscape experience so far. While I once also auctioned one of those for real cheap it seems to be death as not even JTAG having helped me...
I guess just try tftp-booting some such initramfs image for a start.
I am interested in this as well. Since WD stopped supporting the MyCloud Gen 1's, I've been wanting to convert them to OpenWrt since I already converted my WD MyBook Live drives to OpenWrt.