Again, we have open source tools that will generate, mangle, introspect, disassemble, etc. to both ELF and PE binaries.
What PDF is not is the "preferred format for development", no matter how good the open-source tooling is.
No one here is saying that an open-source project to assist with Hyperloop could not be launched. Nor that the ability to edit the whitepaper that was released has anything to do with this proposed open-source project. Nor even that people typically release whitepapers only in LaTeX format.
However if an open source project will be launched with Hyperloop then its success will be at least somewhat dependent on the ability of participants to meaningfully contribute.
If "contribute" just means discussing key points then a simple Wiki might suffice. However if "contribute" means technical designs, then the actual drawings and data will be what's needed, not glorified screenshots of AutoCAD and MATLAB.
With that said, it's not hard in this case to C&P to something more suitable for GitHub and really get things kicked off, but LaTeX would be more suitable.