Unless Mazda decides to remove JCI Test Mode completely from firmware this tweak should work on any firmware past and including V59, certainly worked on my 411A.
JCI Test Mode was only removed from UI, but functionality is still there. Looking in firmware 55.00.753A I was able to find original diagnostic app in /jci/gui/apps/diag. Code to access menu with 20 second press on DEL button is in controls/Test/js/TestCtrl.js, actual app functionality in js/diagApp.js. Between 55.00.753A and 59.00.441A diagApp.js was not changed at all, but UI part - TestCtrl.js - was altered to, among other things, remove access to test mode.
Attached file is a zip archive (rename it), files from it should be placed in /jci/gui/apps/diag overwriting existing ones (better make backup first). Doing so will bring back test mode by adding "T/M" button next to ENTER, single press on which (no need to hold it) will activate familiar test mode. Typing 11 and pressing ENTER later on opens well known test menu.
Perhaps this can be incorporated into AIO as another tweak.
As usual, use AT YOUR OWN RISK.
P.S. Unrelated to the above there is a way to open terminal window right on CMU itself and use USB keyboard to access shell: YouTube video id "M-iJLuxwfzU", can't post link. But I haven't tried it yet.