Math alignment comment in ConTeXt not working as expected

The solution is incorrect since it does not correctly answer the question. The answer seems to be that the stretching of the alignment doesn't work due to a now-solved bug in ConTeXt mkiv.

Something like the following?

\starttext
Here is some text
    \startformula
        \startalign [m=2, align={left,middle,right,left}, distance=0em plus 1 fil]
            \NC \NC \NC 12(x-1) + 20(y-3) + 14(z-2) \NC = 0 \NR
            \NC \text{which is same as } \NC \NC 6x + 10y + 7z \NC = 0 \NR
        \stopalign 
    \stopformula
\stoptext

which results in See the ConTeXt wiki.

You can change the space around the equation using spacebefore and spaceafter keys for setupformula. Here is a complete example:

\definemathalignment
  [flalign]
  [
    m=2, 
    distance=5em plus 1 fil,
    align={right,left,right,left},
  ]

\setupformula[spacebefore={none}]

\showframe
\showgrid


\starttext

Here is some text
\startformula \startflalign
  \NC\NC \NC 12(x-1) + 20(y-3) + 14(z-2) \NC = 0 \NR
  \NC \text{which is same as } \NC\NC 6x + 10y + 7z \NC = 0 \NR
\stopflalign \stopformula
\stoptext

which gives