I watched the Which? road test of the F30 and they said the folding rear headrests was a 'must have' option, however I haven't found rear visibility with the fixed headrests to be a problem. Maybe it's different in the F31?
2012 F30 328i Lux', 8SAT, Melbourne Red
On order:F30 340i M Sport, Estoril Blue/Oyster