I'm less concerned about transit and walking routing (because I am sure Apple will get there), but more concerned about search of maps. OSM search is currently nowhere near the level of Google maps search.
On google maps I can search for things like "usps near south lake tahoe" and it do what I expect. Try that on OSM, or anything remotely not a well formed address. Google maps has some sophisticated logic for biasing towards current location, and it knows the names of places, like 'moscone center', or 'facebook offices'. And of coruse, I cna mispel them all and it still find it.
If Apple maps can't do the same, then no matter how pretty the 3D view is, it will disable one of the main (for me) functions of the device.
I've switched from iPhone to Android and back to an iPhone again, and the only things I liked better about the Android were Swype and the Maps. The iPhone app is at least now servicable. The 6.0 will break it for me (I use transit directions all the time), so I'm left hoping Google saves the day.