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I've skimmed through now.
My view is that actually convergence is the only thing that may become the selling point someday. Of course there is a number of obstacles which I also listed in my post.
Why? Well, without convergence how does Ubuntu differ from Android or iOS?
It's free, open source, privacy focused. But Sailfish is too, Firefox OS was as well. None of them succeeded as well. Given the Android and iOS have so many users, unfortunately few people care about those.
It more tweakable and less locked. Well, hardly a good selling point as well, unless its target are developers only.
It has different UI, navigation patterns. Again, it depends on individual preferences. Existing Android and iOS users may be very hard to move away from OSes they are used to.
The entirely new thing you can do with your phone
I believe that mobile market is a very hard one and the only way to jump in and get a significant share is to find a niche where noone is present yet - and to show people that with Ubuntu Touch they can do things which they cannot do neither with Android, nor with iOS etc. I don't mean things that they cannot do this way or that good, that fast, etc. I mean a quality change - things that they cannot do at all. I see convergence and an option to ditch laptop for some people such a thing.
Relased before it was ready
Also please note the other reasons that are mentioned in the post you linked: convergence was marketed as it was actually done and ready, but in fact it was far from it. Unity 8's functionality is far from finished for desktops, UITK as well, many desktop apps looked bad or didn't run properly when M10 tablet went on sale. I think that was a huge mistake to try selling convergent devices without having delivered the minimum viable product in terms of convergence.
Hardware
And again, the hardware. As Miracast has failed as an alternative to HDMI and few phones provide the MHL, the convergence usability is limited with what we currently have. No to mention the problem of convergent mode with charger cable plugged in. This is why I said that we are not there yet and the correct way is to sell the convergence is to make it work flawlessly first, then create the device that allow users to use the full potential of convergence and then market it and show off the value that convergent phoneputer adds to their lives.
Ubuntu Edge
On the other hand - Ubuntu Edge didn't get funded, but it has actually broken croudfunding record gathering more then 12 million dollars. I believe that the goal was set extremely high (and probably needed to be in order to make it happen), but still the traction it gained hints that there might be a future for converget devices or phoneputers.
