@dazld @alandipert @flyboarder
Thanks for the help guys, I got it to work by uninstalling the homebrew boot version and using the one-liner install script from the main repo.
Exactly what homebrew was doing that led to boot not take BOOT_JVM_OPTIONS and BOOT_JAVA_COMMAND into account is still unknown.
Not going to spend the time to find out what the problem was exactly, but should you need a quick test for finding out if your own installation suffers from the same problem, run BOOT_JAVA_COMMAND="/bin/nothing" boot repl which should exit immediately.