The reflex diffuser has been the standard F1 diffuser for years. These "steps" at the throat of the diffuser might have been introduced by Ferrari back in the day but my memory is struggling to remember when - 2000 perhaps?
Anyway, they've been around a good long while. Here's a Merc one from above looking from the front. You can see how the diffuser steps up very abruptly. Couldn't find a decent image from below.
You get an abrupt step at the throat and then a relatively horizontal section and then the upcurved exit. It appears to be able to perform like a much taller traditional gentle diffuser throat.