A while ago, I designed a syntax supporting colspan (the last pipe of the line being optional):

    || are  easier   | than   |
    | any | markdown | flavor |

The number of consecutive pipes would increase the colspan value. I think I also had support for rowspan but I don't remember how.

The XWiki syntax [1] also supports it by letting you use HTML attributes.

   |=Title 1|=(% style="background-color:yellow" %)Title 2
   |(% colspan=2 %) Word 1 Word 2

Arguably more clunky and less intuitive, but more powerful I guess.

(disclaimer: I work for XWiki)

[1] https://www.xwiki.org/xwiki/bin/view/Documentation/UserGuide...