There are two long-standing questions underlying this discussion.
1. Can present LaTeX users learn to write well-structured user-level LaTeX?
2. Can well-structured markup be written in a GUI?
I believe the answer to the first is "yes". For one thing, I think the LaTeX being submitted to arXiv (arxiv.org
) is improving. I commonly look at arXiv source and try to run it through tex4ht toward html+mathml with mathjax. I see success there as a sign of well-structured LaTeX. But I've not made a systematic investigation on this point.
I hope with user-level documents in LaTeX3 that on-target pertinent markup diagnostics (without obscure package or engine diagnostics) will keep users honest. Of course, in order to maintain service on old documents, this should only be the case for users who ask for it.
As to the second question, my opinion is that a user who understands well-structured markup might be able to generate it in a suitable GUI, but a user without such understanding will not be able to generate good markup. For example, the naive user would be able to write something that appears formatted as an enumerated list, but without invocation of a list-making widget in the GUI, it won't be a list.
Personally, I expect that I would find using a GUI to be inefficient.