MikeMondy

Sure, porting source code from 32-bit to 64-bit is often straightforward. That's not what's happening here. They're using and modifying (hooking into) a compiled binary. One that uses object oriented C++ code complete with lookup tables to indirectly reference virtual member functions and all sorts of stuff that can be difficult to figure out when you have disassembled machine code instead of human readable source. However, de-compilers do exist. I haven't used them, but I imagine that they only go so far and that a lot of detective or archaeology work is still needed. Based on personal experience, reverse engineering and modifying a binary is orders of magnitude more effort than updating source code and most programmers have no experience in doing this. Writing code would be a very tiny fraction of the effort.

FYI, the oldrim version of SKSE does include the sources in the archive. Someone also uploaded that version to github. I haven't looked at it ... but I have done other sorts of reverse engineering and can easily imagine that someone who wanted to pick this up would discover that figuring out how to tie into the skyrim binary and how to modify its C++ objects would be many many man months or years of effort. I expect that the effort is almost all about playing detective with the skyrim internals and not that much about writing code. So, unless the SKSE authors announce they're dropping the project or many more months go by, I'd suggest against diving into this.