This topic is the continuation of threads "Mounting a .zip file" and "Dokan+7zip = mount many possible archives".
Now 7ZIP ("7za.exe a -r -t7z -m0=lzma2 -mx=9") gives good compression (952 to 263 MB), but can be mounted in RO-mode.
Soon we'll be able to mount ZIP archives with bzip2 and deflate (zlib) compression (952 to 366 MB) in RW-mode.

This breakthrough will allow to create portable programs in one executable file that does not require unpacking!
But we still look variants that theoretically can provide better compression and simple structure for RW-mount.
We did some tests and found that 7zip (7za a 7WIM.wim ./Test) makes excellent WIM (952 to 278 MB).

What else we can try for compress executable files?