In bygone times it would usually be expected that game changing features appeared on high end equipment first before gradually filtering down to more affordable gear. But ever since HD arrived things started to change, with the mid-end of the market seemingly getting abilities last, while the high-end and low-end got them first. High definition is a case in point, with Sony's Cinealta series being unattainable for most, while the consumer division of Sony came up with the HDR-FX1 and the professional variation, the Z1, one of the biggest selling camcorders of all time.
The new feature in iOS 13, on only the most recent hardware it should be added, is the ability to record multiple streams of video and/or photos and audio simultaneously.
This means, for example, that you can record video from both the front and the rear facing cameras at the same time. More usefully perhaps is the ability to record from the rear facing wide angle camera and the telephoto camera simultaneously.
The effect of this is to give you the most effective and compact must-cam setup you can imagine. There are some caveats though. For example resolution on the iPhone XS will be limited to a maximum of 1920 x 1440 at 60fps. So unfortunately on current hardware there is no 4K ability using this feature, although expect that to change once new phones are released.
Speaking of which, if you are a developer who wishes to take advantage of the new abilities - they won't feature in Apple's own built in camera app just yet - you will need a minimum of an iPhone XS or XR, or a 2018 iPad Pro. I'm afraid that even the previous years iPhone X is excluded from this capability, and it is purely down to processing overhead, requiring the A12 Bionic chip at a minimum.
With devices gaining in processing power, as well as the number of cameras they carry, each year, features such as this will just get more useful, particularly if you are a one person Vlogger. The ability to record two simultaneous camera shots on one device has been a dream for some for long time now. Although it will be interesting to see what the real world practicalities are with regard to composition and framing.
This year just gets more interesting as time goes on.