Publishing FPGA bitstream source and PCB schematics is probably ok if it does not include copyrighted Nintendo content (because piracy). Probably best to publish anonymously so big boys kind of give up the prospect of retaliation. Same thing kind of happened with the 360 and RGH.The process of creating a custom FPGA firmware is supposedly easy (I haven't done it myself) but anyone who is capable of doing it isn't willing to open themselves to legal trouble by sharing it. You can't just dump the FPGA firmware from the SX Core because it is protected.
More likely reason some are hush-hush is because of the profit motive of HWFLY and friends.