These two issues then -- which I would summarize:
1. Vertical interlocking of staff objects should be allowed by
default, with an option to disable;
2. Minimum vertical space between objects should be maybe 0.5 spaces,
and anyway user-settable
are somewhere between defects, collisions, and enhancement requests,
depending on your point of view.
Cheers,
Marcus
%%%%%%% revised example: %%%%%%%
\version "2.9.22"
\score { <<
\new Staff \relative a' {
\repeat unfold 3 { a4 a a a }
<< {a4 a a a} \\ {a,8 a a a a a \times 2/3 {a a a}} >>
\break
\repeat unfold 4 << {a'4 a a a} \\ {a,8 a a a a a a a} >>
}
\new Staff \relative a' {
a1^\markup {
\column {
\line {Too much}
\line {vertical space?}
}}
a a a
\break
a^\markup {
\column {
\line {Enough}
\line {vertical space?}
}}
a a a
} >>
}
\layout { indent = #0 }
%%%%%%% end revised example %%%%%%%