How to use regular sans-serif italic/upright greek letter in math mode? about unicode-math HOT 8 OPEN

\documentclass{article}
\usepackage{unicode-math}
\setmathfont[StylisticSet=2]{XITSMath-Regular.otf}
\begin{document}
\[ \alpha + \beta + \Gamma \]
\end{document}

% !TeX program = xelatex

\documentclass{article}

\usepackage[mathsf=sym]{unicode-math}
\setmathfont{XITSMath-Regular.otf}[BoldFont = XITSMath-Bold.otf]

\newcommand{\mitsanseta}{%
  \textit{%
    \fontspec{XITSMath-Regular.otf}[
      StylisticSet = 2,
      Color = red
    ]%
    \miteta%
  }%
}

\newcommand{\msanseta}{%
  \textit{%
    \fontspec{XITSMath-Regular.otf}[
      StylisticSet = 2,
      Color = blue
    ]%
    \mupeta%
  }%
}

\begin{document}

\[ X^\mu_\nu = X^{\mu\rho} \eta_{\rho_\nu} = \mathsf{X \eta \msanseta} \mathsfit{X \eta \mitsanseta} \mathsfup{X \eta \msanseta} \mathbfsf{X \eta} \mathbfsfit{X \eta} \]

\boldmath

\[ X^\mu_\nu = X^{\mu\rho} \eta_{\rho_\nu} = \mathsf{X \eta \msanseta} \mathsfit{X \eta \mitsanseta} \mathsfup{X \eta \msanseta} \mathbfsf{X \eta} \mathbfsfit{X \eta} \]

\end{document}

% !TeX program = xelatex

\documentclass{article}

\usepackage{xcolor}

\usepackage[mathsf=text]{unicode-math}
\setmainfont{XITS-Regular.otf}[
  ItalicFont = XITS-Italic.otf,
  BoldFont = XITS-Bold.otf,
  BoldItalicFont = XITS-BoldItalic.otf,
]
\setsansfont{FiraSans-Regular.otf}[
  ItalicFont = FiraSans-Italic.otf,
  BoldFont = FiraSans-Bold.otf,
  BoldItalicFont = FiraSans-BoldItalic.otf,
  Scale = 0.9,
]
\setmonofont{FiraMono-Regular.otf}[
  BoldFont = FiraMono-Bold.otf,
  Scale = 0.9,
]
\setmathfont{XITSMath-Regular.otf}[BoldFont = XITSMath-Bold.otf]

\setmathfontface{\mathsf}{FiraMath-Regular.otf}[
  BoldFont = FiraMath-Bold.otf,
  Color = cyan
]
% FiraMath-Bold.otf is NOT included in CTAN; it must be downloaded from
% https://github.com/firamath/firamath/releases/tag/v0.4-beta-3.
\setmathfont{FiraMath-Regular.otf}[
  BoldFont = FiraMath-Bold.otf,
  range = {sfup, sfit->it},
  Color = teal,
]
\setmathfont{FiraMath-Bold.otf}[
  range = {bfsfup->up, bfsfit->it},
  Color = orange,
]

\newcommand{\mitsanseta}{%
  \textit{%
    \fontspec{FiraMath-Regular.otf}[
      Color = red
    ]%
    \miteta%
  }%
}
\newcommand{\msanseta}{%
  \textup{%
    \fontspec{FiraMath-Regular.otf}[
      Color = blue
    ]%
    \mupeta%
  }%
}
\AtBeginDocument{%
  \renewcommand{\mbfsanseta}{%
    \textbf{%
      \fontspec{FiraMath-Bold.otf}[
        Color = green
      ]%
      \mupeta%
    }%
  }%
  \renewcommand{\mbfitsanseta}{%
    \textbf{%
      \fontspec{FiraMath-Bold.otf}[
        Color = magenta
      ]%
      \miteta%
    }%
  }%
}

\begin{document}

Test \texttt{\textbackslash mathversion[normal]}:
\[
  X^\mu_\nu = X^{\mu\rho} \eta_{\rho_\nu} =
  \mathsf{X \eta \msanseta} \mathsfit{X \eta \mitsanseta} \mathsfup{X \eta \msanseta} \mathbfsf{X \eta \mbfsanseta} \mathbfsfit{X \eta \mbfitsanseta}
\]

\bfseries\boldmath
Test \texttt{\textbackslash mathversion[bold]}/\texttt{\textbackslash boldmath}:
\[
  X^\mu_\nu = X^{\mu\rho} \eta_{\rho_\nu} =
  \mathsf{X \eta \msanseta} \mathsfit{X \eta \mitsanseta} \mathsfup{X \eta \msanseta} \mathbfsf{X \eta \mbfsanseta} \mathbfsfit{X \eta \mbfitsanseta}
\]

\end{document}