Put the offset at the end! Famously, the table of contents of a .zip file are the end rather than the beginning, which has many useful properties (such as being able to patch the contents by only appending to an existing file). And you can concatenate an executable and a .zip and get a file which is both.
Yes. Cosmopolitan libc has support for exactly this. It contains a lot of platform-specific hacks in order to open the executable though. I went through the implementation.
I think the problem is this notion of a "memory image". It would be so much easier if the kernel just copied the entire file into memory and called it a day.
