[LightDestory]

Nowadays smartphone's market is filled by Android & iOS devices, speaking of Android you can find low-mid-high price range.
I don't think that a new OS will likely survive on the currently smartphone jungle. Why

• How many people will buy it? Common smartphone user doesn't know what means "open source" anyway. It will be a products for a very few geek people.
  
• Thinking about the previous point, Do you think developers will port their app on this new OS? Developers don't work for free, if they can't earn any money they will not support it. We got an example from the past: Windows Mobile/Windows 10 Mobile was affected by lack of apps, the few apps that WM's user got were ported by developer with Microsoft Support behind them. 
  
• "Common smartphone user" lives with apps, if you tell someone that on this particular phone there isn't "instagram/facebook/what's app/telegram/ <any mainstream application" it will not buy it. (Please don't count as apps the web form of services such as Telegram Web).
  

We got examples also from the past:

• Ubuntu Touch was a project with the aim to port a Ubuntu on smartphone. It didn't live for long: abandoned by Canonical and then by UBPorts it is now faded away from our mind.
  
• Tizen, born as a smartphone open source OS, currently used only on Smart TV or SmartWatches with very few app available (read the list of disadvantages up there.)
  
• PostmartketOS, it was good project, but currently we don't know how it will end: started as a smartphone OS replacement currently it is a geek linux distro for smartphone that doesn't support any smartphone features.
  
• Sailfish OS, currently the most "usable on daily device" project but still lacks on apps. IT can emulate and run Android apps it doesn't work every time. Don't except to run on it games or heavy apps. What did I forget? Well, It owned by Jolla and the last phone shipped with this OS was on 2016. There are also VERY FEW smartphone supported and almost every planned device is now a ghost.
  

PureOS, the OS that will power up the smartphone of this thread is almost like Sailfish. I can't predict the future but I think it will end like Sailfish.

We have also a example from our time:

• The "new" Huawei OS called HongMeng that was like "hidden weapon" of the OEM it is still an alpha stage for smartphone usage. HongMeng was developed as a TV OS and as a "chinese-market" OS, so they weren't developing any Android emulating for apps because almost every app was intended for chinese people. Huawei is not ready to use it as an Android replacement, in fact on few articles Huawei CEO stated that HongMeng will land of smartphone ONLY if US block will be actived.
  
• Pinephone is like PureOS/SailFishOS. I don't know how it will end but it is another project in development.