I really think Racket's Scribble has a chance to over take Latex. https://docs.racket-lang.org/scribble/
Scribble is well designed to be a more readable Latex with the ability to be beautifully type set.
Example:
#lang scribble/base
@title{On the Cookie-Eating Habits of Mice}
If you give a mouse a cookie, he's going to ask for a glass of milk.
Pandoc is a great tool to use if all you need is Math. http://pandoc.org/MANUAL.html#math
Wow, thanks for the resource... going to give this a go on a current project of mine. Does anyone know of a solution that solves having fairly complex Excel tables? It seems like all of these Latex solutions just have basic text tables...
> Excel Tables?
Are you meaning just having nice looking tables?
If your going more then just nice looking tables I HIGHLY recommend RMarkdown.
http://rmarkdown.rstudio.com/lesson-7.html
Using RStudio with RMarkdown makes amazing looking tables with the package Stargazer.
Except for handwriting based solutions like the very cool Nebo app, I really don't think there is a better way to enter formulas, and it can be learnt in a matter of hours.
Writing complete documents in LaTeX is perhaps a bit more verbose, but then he can use some of the methods suggested here, like pandoc.
Spellchecking he can have if he wants, and even WYSIWYG.
It's worth noting also that if you're aiming for a career in math or physics, not learning LaTeX isn't really an option.
EDIT: I referred to the Nebo app as 'MathPad', which is an older incarnation of the same idea, Nebo is MUCH better.