| Linux/Sparc64 binary compatibility under NetBSD/Sparc 64, any success?

Not at the moment.  Actually, there is no Linux/sparc64 that I'm aware of.
The available Linux ports to SPARC V9 machines all run 32-bit userlands.
So you really want Linux/sparc32 emulation, which is more complicated.  It
requires a useable Linux/sparc emulation that works on NetBSD/sparc, then
another layer needs to be added to handle 32-bit -> 64-bit traslations.

Getting compat_linux working on NetBSD/sparc looks relatively easy.  Some
bits already seem to be there.  All you probably need to do to convince
someone to finish it is to find a compelling reason to run Linux/sparc
binaries rather than recompile from scratch.

Adding compat_linux32, on the other hand, would be quite a bit of work,
as you can see from compat_netbsd32, compat_sunos32, and compat_svr4_32.

Eduardo