I’d like to propose an engraving option:/Brackets and Braces/Vertical offset to the bottom end/wing of brackets which are close to treble clefs.
This practice was used in plate engraved music to avoid a collision between the bracket lower wing and the treble clef (see the example below, from Breitkopf). Otherwise, either the shape of the wings needs to be very short, or the distance to the stave has to be universally increased.
You can globally increase the height of the wing with this setting:
… but I presume you want a different offset just for circumstances where they would collide (also C clefs, which could be at high or low positions).
(Though of course it’s questionable what a bracket is joining when there’s only one staff.. 
)
Good point about movable C clefs, which could also collide. For orchestral scores it’s mostly the problem with the treble clef.
