Android has sucked up all breathing space in mobile operating systems. There is no chance for something else.
if we had a hackable open source and libre linux phone, even if the user base were 1 percent or .5%, we would likely start to see shifts in user interface and functionality design on the mainstream platforms-- besides, it'd be super rad to be able to actually use my phone for m0re than mindlessly scrolling 'feeds' and messaging.
as a cash-strapped third worlder constantly on the move in a mega-city, termux has been a huge relief for me and postmarketOS and other players looks promising.
i'd seriously be interesting in commercializing such a device to the raspbi/arduino/developr/hacker crowd. it's got lots of money, lots of clout, is clearly identified, growing and diversifying, and has been proven to spend money on interesting and useful tech. Any takers ?
The issue of apps will always be an issue. No matter what commmunity you go to, most people will probably want at least one of a number of popular apps that won't be on this OS. Some can be reverse engineered or use hidden APIs but not always. Examples being: Messenger, Whatsapp, Snapchat, most other messaging apps or video chat apps like Skype or Viber, Instagram (website doesn't have tagged photos of people or uploading), Pandora, Spotify, Netflix, Hulu, basically any tv sort of app, most dating apps like Tinder, Shazam, and any major mobile games.