Bah! This has been done. About 10 years ago I installed a SuSe Linux because of the promise of ease and usability for morons like me.
I think it was impossible for any linux distro to satisfy windows users "at face value" 10 years ago. I think it still is and should not be a serious goal. However, they have come a very very long way -- I think many of today's linux users would not even recognize an install from 2000. I still don't recommend it to people simply on the basis of "ease and usability"; again, no one can out do windows there (maybe google?) IMO, it's more for 1) the curious, 2) people with certain politics, who are probably more inclined to learn new things, and 3) people who are looking for specific kinds of functionality beyond general "ease of use", eg, webservers, and as a programming environment. Most people don't program or run servers, and it's silly to try to appeal to everyone.
To an extent, it still has the array of "incomplete and/or non-functioning apps", but it's much harder to notice since most of the activities your normal consumer will want to engage in are pretty solid, with a range of choices. Again, this is the nature of the model -- it is not one monolithic group of people trying to deliver a single product to a researched marketplace. Notice, there is 5-10 times more software available in a basic linux install as opposed to what you will get off a windows disk.
There were no instructions for command line operations, working with an unfamiliar desktop where you could toggle between multiple variations was tremendously confusing as were, optional GUIs, and pretty much everything else.
Exactly. This is a consequence of unix style modularity. The command line is almost always the BASH shell, which is it's own piece of software, and of course all the GNU utilities. But GNU is not directly associated with any of the distros; they do provide plenty of documentation (such as man pages), just you need to understand they are independent of the distro. Altho I agree with most of your other points, vis, linux vs. windows, I would strongly disagree with this one -- there is
a lot more high quality documentation for the former. One of my least favorite activities in life is dealing with the flaccid and pathetic windows "help browser".
Also, there is far more variety amongst linux installations than with any other OS, such as the choice of window managers, etc. As you observe, this introduces a lot of potential confusion for newbies used to MS or Mac, where there is just one completely integrated environment.
Every time I went to a user community and asked questions, I got flamed with insults.

they are as reactionary and opinionated as most other people -- if you inadvertently put the wrong spin into your question, you will set someone off about something.
When they make a *nix that's entirely operated through CPanel, I'm in.

Exactly the kind of thing I'm hoping won't happen

The desire to "mainstream" linux is on the surface noble, I guess, but maybe also misguided: too much lowest common denominator

I already hate the new package manager interface.
Then don't use it. They are just front-ends for apt and dpkg (in Ubuntu) anyway -- which every unnecessary level of abstraction runs a risk of adding unnecessary complications. apt couldn't be simpler as is...