It will be available for purchase in 2024

It’ll measure blood oxygen saturation / include a pulse oximetry function.

It will eventually be tied up in litigation like the pulse-ox sensor on the watch

It won't be available for purchase in 2024 

It will be available in a range of colours

There will be a higher memory model sold for more money at launch (think 128MB vs. 256MB models)

There will be a gold version (real gold, not just gold colored)

Improved health tracking if you pair it with an apple watch (ie better data if you wear both than either by itself)

https://www.yahoo.com/lifestyle/rumors-ramp-apple-smart-ring-120908847.html

End date will be changed to match public launch date once announced.