Ability to set left barline of systems
A publisher I worked for from time to time requires systems to start with double bars if the previous previous system ends in one. MuseScore does not allow this - it gives you the option of drawing a barline at the start of a system, but no way to control what *type* of barline is drawn.
See for instance this lead sheet, which was created in Finale:
Note how the third system begins with a double bar - this is done because the second system *ends* in a double bar. This cannot currently be achieved in MuseScore short of drawing a line placing a graphic, but that is an extremely awkward workaround.
Two solutions I can see:
1) An option in General Style->Barlines to control whether the left barline at the start of a system automatically is drawn the same way as the right barline at the end of the system. This option would presumably be greyed out unless one of the options to draw left barlines at starts of systems is selected. No change would be required to the score format as far as I can tell - it's just something that would happen when drawing the score.
2) The ability to set the left barline at the start of a staff in the same way barlines are normally set - select barline, double click icon in palette, or drag icon from palette to barline in score. Setting the left barline in this way should not necessarily affect the right barline at the end of the previous system - you could in theory have a double bar at the start of a system that did not end in a double bar, or a dashed barline to start a system that ended in an invisible one, etc. This solution would require a measure to take an optional additional property to store the left barline style.