If the formatting code of TeX is a bit too awkward - and it certainly is for me - then LyX would seem to be the obvious answer, and it's free. Why not see if you can get some volunteers together to attempt a port of LyX using the UPP libraries? Saying that direct export of LaTeX from a RISC OS app would give a better system than rival platforms rather misses the point, which is that if you use TeX and LyX correctly, you don't do the formatting yourself at all. Having a conventional WYSWIYG WP outputting TeX is ass-backwards, AFAICS.
But I have to agree with those commenters who have observed that TeX seems to be on the way out. I'm working on a book for a Californian publisher at the moment & they insist on MS Word files. Indeed, they even want files from MS Word /on Windows/ - a snag, as I write on a Mac.