It seems kind of mad to think Ubuntu could succeed where Microsoft failed. I just can't see any way they will convince third party developers to write apps for it.
With a "proper" linux-based phone anyone (assuming the hardware isn't crazy locked down) can contribute to the success, even if it remains a niche not everyone cares about snapchat or the hippest app of the month, if I can connect to my work VPN (this is actually where I ended up switching to an iPhone, there's no AnyConnect client for Windows Phone), use an email client with Exchange support, and have a modern web browser I'm mostly set for a daily driver - sure, it's nice to be able to use Netflix, Amazon Video, PlayStation Vue on my phone, but I've got my TV, my desktop or my tablet for all of that.