The DisplayPort standard supports being passively converted to HDMI, but you still need a DisplayPort connector on the source end. This is a weird custom port which can physically accept a DisplayPort connector or a HDMI connector, so you don't need a special DP to HDMI cable, a regular HDMI to HDMI will work.

I'm guessing this isn't more common because the HDMI forum charges a license fee per port, so turning every DP port into a DP/HDMI hybrid would increase the unit cost.