I haven't personally used this feature at time of writing but I can imagine it would be useful for merging in a bootloader, e.g. we have a design that has 3 components:
1. Nordic MBR
2. User application
So may give it a try out in the future.
I imagine users of other devices have similar requirements e.g .with blobs for the ESP32. So I don't see why a working, cross platform feature like this should be removed so that 'users can come up with their own solution', if they want to do that then they can disable the feature and do as they wish already, leaving it in doesn't (as far as I know) cause any issues so why remove it?