For this mechanism to work, the standard electrode potential (SEP) for the Co3+/Co2+ half-cell must lie within a certain range of values as indicated above (+0.20 V to +1.77V). However, the SEP for the half-cell Co3+ (aq), Co2+ ( aq) | Pt is +1.84V. At first glance, you might think that in non-standard conditions this value is not that far out of the range required, but concentration or temperature changes do not alter Capital DeltaE values very much. The main reason is cobalt ions can form complexes with the 2,3-dihydroxybutanedioate ions - a bidentate ligand. Electrode potentials for half-cells involving complexes are often substantially different from those involving simple ions. This is another fruitful area for discussion (crystal and molecular orbital theory).
Unfortunately the value for this half-cell is not quoted in the literature but even if it were shown to be energetically favourable, there would still be no way of knowing whether the reaction was kinetically favourable. You would have to do this experiment to find out. Finally, you should note that cobalt(II) catalyses the decomposition of hydrogen peroxide into water and oxygen and the equations written here do not take that into account. Clearly, this side reaction will influence any thermodynamic or kinetic discussion with this reaction.