So we had Jolla, Ubuntu, Mozilla and even Microsoft trying to create a new major player in the mobile OSs market - all pretty much failed to do so. Is it practically impossible? Are we stuck with Android and iOS forever? This tiny selection of options worries me.
I think it's pretty simple: people want to use apps on their phones, and no phone OS is viable without a competitive library of apps.
Most major apps are developed for both iOS and Android, and convincing app developers to develop for a third platform is going to be a tough sell, unless that platform is very attractive to users. However, to be attractive to users, it will have to have a lot of apps already...
I suspect that the only way to gain marketshare for a new mobile OS is to ship it with an Android or iOS compatibility layer, which would be pretty difficult to do well. The developers would have to re-implement the entire iOS or Android API, and keep up with all of the changes. If they did that, there would be no incentive for developers to target the native APIs of the OS, because they could just target Android or iOS like they do already. So, the compatibility layer could never be deprecated.
So yeah, I think we're stuck.