What's the killer feature for your workflow? I don't see anything that gets me particularly excited in their "Differences between make and mk" list.

"11. Alternative out-of-date determination

Sometimes the modification time is not useful for deciding when a target and prerequisite are out of date. The P attribute replaces the default mechanism with the result of a command. The command immediately follows the attribute and is repeatedly executed with each target and each prerequisite as its arguments; if its exit status is non-zero, they are considered out of date and the recipe is executed."

When I want this in GNU Make I end up hacking together something resembling:

  define test-exec
  $(filter OK,$(shell if $1 >/dev/null; then echo OK; fi))
  endef

  define test-docker-image
  $(if $(call test-exec,$(DOCKER) inspect $1,,docker_$1))
  endef

  target: $(call test-docker-image,foo)
    $(DOCKER) run foo ...

  docker_%:
    $(DOCKER) build --force-rm -t project/$* $*

It seems this can be replaced with:

  docker_%:VPdocker inspect: %
    $DOCKER build --fore-rm -t project/$stem $stem