So, gramma goes to a web page, clicks the signup, the website deploys a docker image on a webhost and spins up a UI that is not unlike what she is already used to.
Next, comment and "likes". You have to have a comment system that runs on there also. Gramma would invite others to her site by clicking invite. This would generate a specific invite signature for that person and would email it out (gramma would need to know Uncle Fred's email; sorry gramma). Uncle Fred would click the link and be taken to gramma's sight and can comment. All comments stay on gramma's sight. All gramma's content, period, stay's on gramma's sight.
How does one monetize, however?
With a docker UI like Kitematic, it's remarkably similar to an app store experience.
I get what you are suggesting, but I can't help but to think you are making this way bigger issue than it actually is.
Also all of you are missing the most obvious point: if it hasn't happened to a lot (and I mean literally more than 10-20% of user base) it is not a significant risk and thus spending extra effort for literally no gain (and actually probably more of a loss in views/users/buyers/whatever) is not worth paying someone to design you a website and paying for updates and then A) paying for (yet another) 3rd party company to host your website B) learning how to setup, host, update, and maintain your own website.
I'm sure most of people on this site could easily setup their own website and run it wherever, but the reason why people are paying you to do such things for living means that most people can't be bothered to learn all the necessary skills.
The internet is not crucial to everyones daily life. And honestly, it probably shouldn't be as crucial to ours.