The PinePhone will likely be preferable to most LineageOS phones, since it will run a closer-to-mainline kernel. It's also expected to be available for a "fraction of the cost" compared to the Librem.
From what I've been seeing, despite the PinePhone having worse specs and not as much privacy focus it's going to absolutely chew up the LibreM 5's marketshare purely because it's more bang-for-buck.
Anbox is a compatibility later that runs Android apps on other Linux distributions. It's not stable yet, but there has been some interest in adding Anbox to mobile Linux distributions like UBports and LuneOS.
I doubt that this would be nearly as useful as you think since so many apps are dependent on Google services these days and even the client libraries for them are proprietary. And then there's the fact that you're constantly playing catch up with what is effectively a closed platform with no real public roadmap that throws the occasional source drop over the wall and says 'good luck!'
It's unlikely today's Google is going to be interested in seeing these efforts succeed. So an Android app runtime would likely only really run software from 5+ years ago well. Better to focus on making a really solid Linux mobile experience, IMO.
How do you know how useful I think it will be and in what ways?
F-Droid exists. People installing APKs exist. In some cases these options are better than literal nothing, and especially if momentum builds around these it's possible that app developers may notice.
For lineage, it is popular to install Google Play anyway. I guess that to be a copyright violation that Google looks the other way for and if a real world competitor did this they would crack down.
Yes, but they are not working hard. Even if they had the runtime, they won't have apps because google won't give the access to the play store, so what is the point of the runtime?
I've seen 3 projects working on the runtime (in 3 different ways with different pros/cons).
