Ok - I fail to see how this is news. Cygwin has provided Gnu tools in windows forever. Cygwin-X has provided X11 in Windows forever.
SFL and Cygwin have drastically different performance profiles.
SFL is syscall translation in kernel space running on pico processes; Cygwin is syscall emulation in userspace running Windows processes and Windows threads.
Windows is built around an object oriented philosophy (handles) where, for instance, access rights are established upon handle creation. Handles covers many more types of resources in Windows compared to e.g. file descriptors or inodes in Linux. But the key difference is in lifetime. Under Linux access rights are checked on each access. Under Windows you request access rights on handle creation, a jump table is established with an entry for each operation - some of them pointing to "access denied" - and hence Windows does *not need* to check rights on each access. Now, if you want to emulate Linux inodes/fds, you would need to create/dispose the handle on each access, or design some system with cache/sweep. Either way you are going to sacrifice some performance. And this is just one example.
SFL uses pico processes which do not own Windows handles the way Windows processes do. It is Linux like processes running on top of pico processes. I believe the real work for MS has been in the areas where those processes touch the same interfaces (such as file system) which must allow for the Linux way of accessing resources.