It also allows building packages for different Arch based distros on the same host more easily.
Arch Linux 32 has the same issue and solved it using this much simpler patch: https://github.com/eli-schwartz/devtools/commit/c0681c0ec0a93a4a4eaf9b2fd85c...
The solution would then be to add the different cachedirs to the pacman.conf you use, which is anyways going to be different due to being i686-specific.
But this will still bind a directory from the host into the container right? It would require me to create separate cache directories on the host and create matching pacman.conf files. It would indeed be a simpler patch to devtools, but the whole process is harder.
This is inevitable if you want to have a cache which persist through cleaning the root/ chroot (the option is -c, IIRC) - which is IMHO a good thing to have.
I do think these patches make sense.
Only if you plan to use no (persistent) cache at all. regards, Erich