Indicator for unclear repeats
I don't know if something like this has been suggested already, but it would be nice if there were some kind of indication that the starting point of a repeated passage is unclear and not likely to work properly. This commonly happens if the passage to be repeated hasn't been enclosed within two corresponding repeat signs. Sometimes this even affects repeats in unrelated sections of the score. It's an easy thing to fix, but sometimes it can be hard to trace, especially if the score is long and consists of many repeated sections.
What I had in mind would work in much the same way as the coloring of notes that are beyond an instrument's range. The mismatched or unmatched repeat sign could call attention to itself by changing color.