There is currently no way to write a bold italic capital Greek letter (e.g. for angular velocity vector) in MediaWiki Math. Combining \boldsymbol {\mathit \Omega} outputs just a non-bold italic version of the symbol (and combining \mathit {\boldsymbol \Omega} outputs just a non-italic bold symbol).
The easiest way to achieve a bold italic capital Greek symbol in MathJax is to use e.g. \boldsymbol \varOmega which is already supported by MathJax, but the Greek variable macro is not recognized by texvc, so the syntax is rejected. (In LaTeX, we might also choose to use \bm {\mathit \Omega} instead, but this requires \bm from the bm package, which is not currently supported by MathJax, so it would be more difficult.)
So I propose to add all symbols for capital Greek italic symbols (i.e. \varDelta, \varOmega, …) supported by MathJax (see https://docs.mathjax.org/en/latest/tex.html#v) to the list of supported macros in Texvcjs.