I share some of the same observations that seem to have motivated this project, but my solution was to just use Alpine on the same architecture as the target (possibly via qemu) and then export a subset of it to a filesystem image. I implemented it as a perl module collection with no dependencies other than core perl modules, and then run the export from within the image itself. Among other things, it lets me use strace to find the runtime library dependencies of the things that need to be in the image.
https://metacpan.org/pod/Sys::Export