Cross-compiling Samba is a nightmare, and the Samba devs are providing zero assistance there ("if you get a working WAF build profile, feel free to send it to us" was the conclusion they posted on their mailing list a few years ago). Plenty of folks tried to get 4.x to cross-compile on non-x86, with no real luck with it. Personally I simply gave up both times I tried to.Nothing to keep it off ARM except for resource restrictions - it's a bit of a beast...
You basically have to provide your own answers to everything that is normally handled by autoconf, which requires you to be a complete expert in *IX environment.
Samba probably has the worst build system I have ever seen out of an open-source project. So I'll be definitely keeping an eye for a final release from Netgear, and hope they provide the build files for it.
Meanwhile, Asus is just starting to get Samba 3.6. Something I've done years ago, they could have saved a lot of work by just grabbing my code. <shrug>