And just like TSA locks, the bittings will leak, rendering the lock useless to all but the laziest adversaries.

What do you mean 'will leak'? You can find pictures of the master keys online today.

I think the TSA locks are a great example of why backdoors are completely idiotic.

That was exactly my point. The TSA lock bittings are available and the back door keys will be available shortly after instituted.

Think about the threat model for a lock on a suitcase. The adversary must have your bag in their possession. It's the perfect example of something that's only to keep honest people honest. Also, they make sure that your bag stays closed.

Does anyone actually use a suitcase that while locked with any padlock can't be opened with a pen?

Unless the lock is secured to something other than the zipper you can resecure it invisibly too.