Well the way i see it..
They've purchased all the patents from Microsoft somewhere mid to the end of last year, including those for the Lumia camera UI.
Developing the Pro Lumia app for Android takes time, but they had to jump into the smartphone game since competition has no mercy lol.
They've established themselves on the market again, and can now fine-tune the software.
The Pro camera app will be available in every ZEISS equipped Nokia smartphone, including the Nokia 8, as confirmed by Juho Sarvikas on Twitter : https://beebom.com/nokia-pro-camera-app-to-arrive-soon-on-nokia-8-confirms-hmd-globals-juho-sarvikas/
So have some patience, yes it's taking a long time and a camera update is long overdue, but it'll pay off i'm sure. The camera samples from the Nokia 7+ and Nokia 8 Sirocco are looking great from what i've seen.
In the meantime i've been using a google camera port from Arnova here, takes decent shots, so maybe give that a go for the time being : https://www.celsoazevedo.com/files/android/google-camera/