Plasma Mobile has the right idea. Build the platform, let communities form around the layers above it (and below it) and just try to get people working together on one goal (especially since all these mobile OS projects are all using Qt, all using Wayland, all using Linux). Lets just hope the KDE guys don't vaporware this one like Plasma Active, it sure would be lovely if Unity 8 got rebased on top of it, and used xdg-app like the community is pushing towards. Firefox could even get in on it as the default browser with great integrated webapp support.
Also it sounds like your comment is technical point of view. Users dont care of that. If mobile system cannot attract regular users, then it is dead.
If you don't get on Sprint / AT&T / Verizon / Tmobile store shelves you are DOA before you even think about appealing to users switching.
But something like Plasma Mobile does not need to care too much about that. If it has the technicals right, and can run Android apps, it can be an enthusiast platform nobody else adopts because Google has strong armed manufacturer control to keep that kind of competition off store shelves if they wanted to. Its also incredibly expensive to buy market share like that, something none of these participants have the money to do.
Since we took the opposite approach, focused on product first and demonstrated user traction and sales the stores and carriers came to us to talk and it changed the whole power dynamic.
Every year brings several new mobile brands to the market. Most you will never hear of because they're not exciting or special. They don't focus on making users excited about their unique product, rather they focus on business deals that even if they go through end up in no sales.
This might be so in US, but in most European countries we buy our phones ourselves with pre-paid options.
Firefox OS seems to be something between Android and IOS. They are trying to solve all the problems of those two but on the end are just average. Just another OS that really looks like Android for regular user.
Redesign everything and rethink the basics - go the way Windows Phone went, but with open environment and much more developer friendly space. Widnows Phone is an amazing piece of UIX and with great ideas, but it failed regarding supporting developers and making its store user friendly. This is where Firefox should aim, not another "better" version of something everyone knows to well.