Feature request: revert in another context

[Simon Albrecht]

\version "2.19.49"
%{
It would be formidable if in such a case one wouldn’t need
to look up the default stencil procedure, but could use either
\undo or \revert.
Is this a valid/sensible feature request?
%}
\score {
  \new PianoStaff \with {
    \omit SystemStartBrace
    \accepts GrandStaff
  } <<
    \new GrandStaff \with {
      % those don’t work
      %\undo\omit SystemStartBrace
      %\revert SystemStartBrace.stencil
      % this does
      \override SystemStartBrace.stencil = 
#ly:system-start-delimiter::print
    } <<
      \new Staff { 1 }
      \new Staff { 1 }
    >>
    \new Staff { 1 }
  >>
}