You really need the person who did the work to elaborate but it is my impression that there isn’t a significant functional change with this but rather just getting the current support out of the Purism-specific changes and into the mainline - so, at least as far as this specific hardware component is concerned, you could run Debian on your phone instead of PureOS. This improves choice and long-term stability and support for the Librem 5. This could also reduce the lead-time between a new Debian release coming out and the corresponding PureOS release coming out for the Librem 5. In theory it also helps any other hardware device that is using this (poorly documented) NXP chip (and using a camera).
Again, beyond my pay grade, but I believe that this is unrelated. It perhaps depends though on what you are referring to. Link to existing discussion?
AIUI, the basic idea is that most existing Linux software expects a webcam that interfaces via USB (i.e. a UVC class device). The cameras on the Librem 5 (and also on the Raspberry Pi) use CSI and not USB. So to make existing software play nicely with both types of camera interface, you either need to emulate (bridge the software gap) so that the CSI camera also looks like a UVC camera or you need to introduce a higher level interface that hides (blurs? 
) the differences between the two interfaces (supporting both underlying hardware interfaces) and change software to use the new interface or do both. I don’t know which if any of those is happening. But that may not be at all what you are referring to???