\definefontfamily[mainface][serif][Brill] %[TeX Gyre Termes]
[protrusion=quality,
expansion=quality,
mode=node,
force=yes,
]
\definefallbackfamily[mainface][mm][TeX Gyre Pagella]
[preset=math:digitsnormal,features=f:oldstyle,scale=0.94]
\definefallbackfamily [mainface] [mm] [Brill] [preset=math:lowercasegreeknormal]
\definefallbackfamily [mainface] [mm] [Brill] [preset=math:lowercasegreekitalic]
\definefallbackfamily [mainface] [mm] [Brill] [preset=math:uppercasegreeknormal]
\definefallbackfamily [mainface] [mm] [Brill] [preset=math:uppercasegreekitalic]
\definefontfamily[mainface][mm][TeX Gyre Termes Math][scale=0.94]
\setupmathematics[ucgreek=normal,lcgreek=italic]
\setupbodyfont[mainface,10pt]
\starttext
0123456789
math: \m{0123456789}
δ\quad\emph{δ}
math: \m{\delta} \m{δ}\quad should be slanted
π\quad\emph{π}
math: \m{\pi} \m{π}\quad should be upright but slanted will do
Π\quad\emph{ Π}
math: \m{\Pi} \m{ Π}\quad should be upright
\m{2+2=4}
\startformula
\sin{α}={{ΑΒ}\over{AC}}=\sin{\alpha}
\stopformula
\stoptext