Music sheets have a warning change of key (or time) signature at the end of a line if that change begins in the first measure on the next line. This is invaluable for sight-readers. Notation composer should have this feature (if it doesn't already). If this feature is enabled, then it will have to show these automatically since scores are constantly editted causing the measures to move around.

And an unrelated suggestion: Arpeggios that go across two staves. This is quite common, but can't be done on Notation composer.