The only strategy that could lead to GNU/Linux [Ubuntu] being adopted by a large number of users is to do what Apple has done with the "Mac" : sell specifically assembled computers with a distinctive brand (e.g. the "Tux") and build a user-friendly brand-image through marketing.
1. Harware compatibility is the number one problem
I've been installing Ubuntu on friend's computers since 2010. I installed 12 different machines (4 desktops and 8 laptops). I had various harware compatibility problems on 75% of these machines ! (mainly related to GPU, Wifi, Bluetooth, ACPI (suspend), brightness, keyboard special keys, touchpad, kernel mei module and black screen on the first run). Plus compatibility problems with peripheral hardware (smartphones, printers, scanners, TV tuners...). This is exhausting. (And people are not won for Ubuntu : when a friend buys a new machine I have to do the job again.) I do it only because I am highly motivated. Highly motivated people are scarce, they cannot change significantly the marketshare of GNU/Linux.
It is not true that ordinary users can simply download and install Ubuntu easily on their machine. This will never happen because new hardware are constantly been released without Linux compatibility.
Ordinary people will never buy PCs to install Ubuntu on it. (Ordinary people never install OS anyway !)
***Ubuntu need to be sold pre-installed on 100% compatible harware.***
But this is not enough, people will not buy PCs with an alternative OS on it. People buy PCs with Windows because they know it and expect it to work 100% (or they install a cracked version of Windows on their new PC) - or - if they can afford it - they buy Macs*.
*In the last years a lot of people have switched from PCs to Macs. This was a lost opportunity for GNU/Linux. But it is not too late.
***Ubuntu need to be sold pre-installed on 100% compatible harware that has a distinctive GNU/Linux branding.***
Let's call these machines "Tux". There should also be Tux-certified peripherals or even Tux-peripherals.
When these machines are available in stores, then people will have the choice to buy either PCs, Macs or "Tuxes".
Why would people buy Tuxes rather than Macs or PCs ?
2. GNU/Linux is unknown or has a "designed-for-geeks" reputation
They will buy them if a succesful marketing campaign convinces them that :
- Tuxes are as innovative, stable, user-friendly and cool as Macs ;
- Tuxes are even better than Macs because they bring more compatibility with other systems and more freedom ;
- It should also be clear that "Tuxes" are fully integrating with Ubuntu phones and FirefoxOS phones.
Tuxes then should sell better than Macs because they will be cheaper. (Tuxes should be at the same price as PCs or a little higher.)
Apple is the most successful business in the world. Mostly because they were very succesful in building a brand-image.
We have the OS to do better than them. What are we waiting for ?