More like 5 pin DIN connectors (MIDI) but different. If you take a lot at old electronics you will see things for the first time.

Wouldn't that be too big? A typical failure point of all my wired headphones/buds has been the connector or whatever the connector plugs into. A bigger connector creates more leverage, which in turn creates more force, which has been a problem. So for mobile usage, wireless audio seems to just eliminate a whole range of problems and failure points, so it's not all good to use physical connectors?

Connectors break because the materials are cheap, not the force per se. Size doesn’t really matter.

I've had a ton of old headphones and I've never seen something like a 5 pin DIN connector. The old IBM keyboards do use a 5 pin DIN though.

Old keyboards in general if I remember correctly, and mice.

Keyboards yes, mice no. XT and AT keyboards had a big DIN plug until the PS/2 popularized mini DIN for both keyboard and mouse.

But in the XT/AT days mice just connected to the serial port with a 9 pin D sub. Mice weren't all that common in those days anyway as most programs were still text based.