Naturally we'd like the buckle to fail jammed rather than fail open, but why must it be a binary solution set?

How about option 3: Doesn't fail or jam under a survivable crash loading.

To unlatch while under a load may be asking too much for an automotive style pushbutton release, but the "aircraft style" ought to provide more leverage.

Honestly, current automotive safety systems are so much Mickey Mouse. Race cars don't have airbags or belt tensioners. They have a real harness with a real latch. Yes, I know that's "more expensive" but then again, how much do air bags cost these days?