I have been enjoying running Alpine's userland in a Linux user
namespace on a non-Alpine host system.  I create the namespace via a
utility I wrote that I call "lxroot".  lxroot can be thought of as an
alternative to chroot that does not require root access.  (This is
possible because Linux user namespaces can be created without root
access.)

If anyone is interested in learning more, lxroot is here:
https://github.com/parke/lxroot

One potential use of lxroot would be running (as non-root) multiple
versions (and/or multiple instances) of Alpine's userland on top of a
single kernel and host system.  This might be useful for package
development and testing.

lxroot can also limit access to the file system, and can optionally
deny network access.

(Aside:  I have not tried running lxroot on top of Alpine's kernel, so
it may or may not work.  lxroot requires, obviously, that the host
kernel has support for Linux user namespaces.)

Cheers,

Parke