Muy interesante el artículo The Languages Which Almost Became CSS que dice:
When HTML was announced by Tim Berners-Lee in 1991 there was no method of styling pages. How given HTML tags were rendered was determined by the browser, often with significant input from the user’s preferences. It seemed, however, like a good idea to create a standard way for pages to ‘suggest’ how they might prefer to be rendered stylistically.
But CSS wouldn’t be introduced for five years, and wouldn’t be fully implemented for ten. This was a period of intense work and innovation which resulted in more than a few competing styling methods which just as easily could have become the standard.
While these languages are obviously not in common use today, I find it fascinating to think about the world that might have been. Even more surprisingly, it happens that many of these other options include features which developers would love to see appear in CSS even today.