Without reverse engineering, there is no security. No way to find new bugs and vulnerabilities or confirm it's backdoor free. Just blind trust only.

Reverse engineering prohibitions are the dumbest things.

Let's say I do this. Arduino sues me. Okay. Now what? What money are they going to take?

Hell, this would be a perfect time for everyone to form an LLC and purchase Arduinos as the LLC and then release your research under your corporate name as CC0. If your LLC has no revenue, you as an individual are legally protected.

Arduino can try to put the genie back in the bottle but good luck.

Better companies than Arduino have tried to prevent hardware reverse engineering and have failed. Apple being the biggest company I can think of that have tried to sue people for releasing schematics of their motherboards.

It's still legal in Australia, at least, we never got the anti-circumvention rule the US media companies got into the US trade agreements

Or rather we did, but they have exceptions that cover just about every otherwise legal use case. I can legally decrypt media to play on my Linux machine, for example. I think the only thing we can't legally do is circumvent controls to do copyright violation