In the following example, the line and text should be aligned to the middle  when LMTX converts the SVG figure using MP. (Note that you may have to install Roboto, but the font isn't the issue.)

% SOF
\startbuffer[svg]
<svg
   width="25mm"
   height="70mm"
   viewBox="0 0 25 70"
   xmlns="http://www.w3.org/2000/svg"
   xmlns:svg="http://www.w3.org/2000/svg">
  <path
     d="m 12.500001,63.971412 v -12.4787"
     id="path2"
     style="fill:none;fill-opacity:1;stroke:#000000;stroke-opacity:1" />
  <text
     x="-48.831322"
     y="15.60547"
     id="text4933-8-6"
     transform="rotate(-90)"
     style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:12px;font-family:Roboto;-inkscape-font-specification:'Roboto, Normal';font-variant-ligatures:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-east-asian:normal"><tspan
       id="tspan159594-1"
       x="-48.831322"
       y="15.60547"
       style="font-style:normal;font-variant:normal;font-weight:normal;font-stretch:normal;font-size:12px;font-family:Roboto;-inkscape-font-specification:'Roboto, Normal';font-variant-ligatures:normal;font-variant-caps:normal;font-variant-numeric:normal;font-variant-east-asian:normal">16p13.3</tspan></text>
</svg>
\stopbuffer

\starttext
   \placefigure[]{}{\includesvgbuffer[svg][conversion=mp]}
\stoptext
% EOF