The aim is to get as much math using the Brill font as I can.

I currently have:

\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

Two problems:

1. I am not getting slanted lowercase Greek in mathmode.

2. I should like to have all the math lettering in the Brill font. But simply setting the Brill font as my math mainface runs into more problems—I still do not get lowercase Greek and it not only messes up 2+2 =4 , it also reports the error—Math error: parameter \Umathquad\displaystyle is not set—when it comes to the display math.
 
 
My efforts to figure this out have not been successful thus far, so any suggestions will be most welcome.

Alan