This feature would add very significantly to my enjoyment of Soulver.

Just throwing an idea out there; absolutely no idea how well this would work in practice:

Rather than using syntax—which has to be learned—perhaps Subtotals could be collapsed, so that every line which makes up that Subtotal can be minimised to one visible line. (Kinda the reverse of what code editors to, since subtotals are at the of its constituent lines.)