There is a Substratum add-on called "Andromeda", which allows the Substratum Theme Engine to operate without rooting. I hope HMD will make use of this opportunity to create a consistent Nokia look and feel on Android Oreo..
To put it in the words of Seth Godin:"In a crowded marketplace, fitting in is a failure. In a busy marketplace, not standing out is the same as being invisible."
With Google stock Android Nokia fits in and doesn't stand out.
Particularly if the default is Google Material Design and the Nokia Support App in Nokia Design.
@Simon: In the current Android ecosystem, the most successful ones are those that offer an integrated user experience (e. g. Samsung) and the most unsuccessful ones that offer a "Stock Android" (e. g. HTC).
The above mentioned Substratum and Andromeda provide HMD with the opportunity to offer Nokia Look&Feel on Nokia devices without changing the underlying Android (Oreo).
HI Nokia, please give us theme option to install new themes. so we can customise UI..