My reference to X11 was mostly rhetorical, to tell the story. I learned at some point that the reason X11 wasn't adopted, at least in the realm of business apps. I was in, was that it was considered a security risk. Customers had the impression that http was "safe." That has since been proven false, as there have been many exploits of web servers, but I think by the time those vulnerabilities came to light, X11 was already considered passe. It's like how stand-alone PCs were put on the internet, and then people discovered they could be cracked so easily. I think a perceived weakness was that X11 didn't have a "request-respond" protocol that worked cleanly over a network for starting a session. One could have easily been devised, but as I recall, that never happened. In order to start a remote session of some tool I wanted to use, I always had to login to a server, using rlogin or telnet, type out the name of the executable, and tell it to "display" to my terminal address. It was possible to do this even without logging in. I'd seen students demonstrate that when I was in school. While they were logged in, they could start up an executable somewhere and tell it to "display" to someone else's terminal. The thing was, it could do this without the "receiver's" permission. It was pretty open that way. (That would have been another thing to implement in a protocol: don't "display" without permission, or at least without request from the same address.) Http didn't have this problem, since I don't think it's possible to direct a browser to go somewhere without a corresponding, prior request from that browser.
X11 was not the best designed GUI framework, from what I understand. I'd heard some complaints about it over the years, but at least it was designed to work over a network, which no other GUI framework of the time I knew about could. It could have been improved upon to create a safer network standard, if some effort had been put into it.
As Alan Kay said elsewhere on this thread, it's difficult to predict what will become popular next, even if something is improved to a point where it could reasonably be used as a substitute for something of lower quality. So, I don't know how to "bring X11 back." As he also said, the better ideas which ultimately became popularly adopted were ones that didn't have competitors already in the marketplace. So, in essence, the concept seemed new and interesting enough to enough people that the only way to get access to it was to adopt the better idea. In the case of X11, by the time the internet was privatized, and had become popular, there were already other competing GUIs, and web browsers became the de facto way people experienced the internet in a way that they felt was simple enough for them to use. I remember one technologist describing the browser as being like a consumer "radio" for the internet. That's a pretty good analogy.
Leaving that aside, it's been interesting to me to see that thick clients have actually made a comeback, taking a huge chunk out of the web. What was done with them is what I just suggested should've been done with X11: The protocol was (partly) improved. In typical fashion, the industry didn't quite get what should happen. They deliberately broke aspects of the OS that once allowed more user control, and they made using software a curated service, to make existing thick client technology safer to use. The thinking was, not without some rationale, that allowing user control led to lots and lots of customer support calls, because people are curious, and usually don't know what they're doing. The thing was, the industry didn't try to help people understand what was possible. Back when X11 was an interesting and productive way you could use Unix, the industry hadn't figured out how to make computers appealing to most consumers, and so in order to attract any buyers, they were forced into providing some help in understanding what they could do with the operating system, and/or the programming language that came with it. The learning curve was a bit steeper, but that also had the effect of limiting the size of the market. As the market has discovered, the path of least resistance is to make the interface simple, and low-hassle, and utterly powerless from a computational standpoint, essentially turning a computer into a device, like a Swiss Army knife.
I think a better answer than IoT is education, helping people to understand that there is something to be had with this new idea. It doesn't just involve learning to use the technology. As Alan Kay has said, in a phrase that I think deserves to be explored deeply, "The music is not in the piano."
It's not an easy thing to do, but it's worth doing, and even educators like Alan continue to explore how to do this.
This is just my opinion, as it comes out of my own personal experience, but I think it's borne out in the experience of many of the people who have participated in this AMA: I think an important place to start in all of this is helping people to even hear that "music," and an important thing to realize is you don't even need a computer to teach people how to hear it. It's just that the computer is the best thing that's been invented so far for expressing it.