Currently you can choose between 32 and 64 Bit when creating a package. It should be possible to compile both at once. Maybe with a 32 Bit Launcher that starts the right Version.
I sencond that. This would be a really handy feature.
Currently you have to compile both seperately and then copy the binaries over from one to the other.
There is a new feature coming (it’s already there, but not exposed in the editor, as it’s not fully ready for prime time) called All Desktop. This will allow you to cook and package for Windows, Mac, Linux in one package. Currently the code has it packaging Win32, but you could have it package up Win64 as well. If you are curious, see Engine/Source/Programs/AutomationTool/AllDesktop/AllDesktopPlatform.Automation.cs, specifically the function called “GetStagePlatforms()”
This would get you most of the way (if you don’t have Mac or Linux binaries already compiled, it just skips them). However, it’s missing the one feature of a “selector/launcher” executable. It does have a “bootstrap” exe that just runs the one hidden deep in Binaries, but it won’t choose 32 vs 64.
It also will compile OpenGL shaders that you may not actually care about if you aren’t released on Mac/Linux.
This does seem to be a good use case of AllDesktop, (or a similar new creation), but work would have to be done in the Bootstrap executable (the source code for that is in UE4).
I don’t have a time frame for such a selector (since I hadn’t thought of it until now), but I can add it to our backlog of features. If someone wanted to bite the bullet and submit a Pull Request in GitHub, that would be welcome!