Everything from thunking layers to calling conventions to inline assembly in the Wine codebase had to be redesigned for this release of Wine; an absolutely massive proposition. Ideas such as dynamic binary translation and running Win32 executables in the MacOS hypervisor framework were considered, and some ideas I tried while hacking Wine gave me insight into other projects I hack on such as Qemu and LLVM.
In short; props to everyone who worked on this! It was a long time in the process!