Hi Carmen,
You can currently get a quantity that is somehow proportional to fibre orientation dispersion using fod2fixel -disp. It’s literally just the integral divided by the peak amplitude of the FOD lobe, so it’s not ‘calibrated’ to e.g. a dispersion angle; but it should be small for sharp FODs and larger for fatter ones.
If you’re an ISMRM member, you can access my 2016 abstract, which presented a more sophisticated FOD post-processing algorithm trying to get at this quantity. It may eventually see the light of day if I ever find the time to get back to it. 
Cheers
Rob