In recent interviews with Reuters and Bloomberg, Arto Numella, the CEO of HMD Global, said that the upcoming devices will be extremely true to the Nokia brand. He praised simplicity, ease of use, reliability and quality, which the Nokia brand is known for.
Also, the reports state that HMD is building its OS in partnership with Google, which could mean a bloat-free Android version for upcoming Nokia smartphones.
“We will be extremely true to the Nokia brand. The Nokia brand is known for simplicity, ease of use, reliability and quality. These are the elements that we will deliver together with amazing industrial design.” -Arto Numella
New Nokia phones will probably use the Z Launcher as the default launcher, but HMD will probably give users the choice to switch to the stock Android UI. All in all, we will have to wait till MWC 2017 for a clearer picture of the OS upcoming Nokia-branded smartphones will be using.