I never implemented that because I feared the additional complexity of dealing with the axis title if it’s left aligned and other edge cases. You can do this manually by scaling your data with the desired factor and placing a label in that spot:
x = rand(100)
y = rand(100) .* 10e10
y_scaled = y ./ 10e10
f, ax, sc = scatter(x, y_scaled)
Label(f[1, 1, Top()], halign = :left, L"\times 10^{10}")
f
