"The LT®8705 is a high performance buck-boost switching regulator controller that operates from input voltages above, below or equal to the output voltage."
A buck boost concept is not that much different than regenerative braking. in both cases a full H bridge is used. In the buck-boost charger, the voltage can be higher, lower or equal and transfer current to the battery.
By using the desired charge profile (fast,slow,float) it will supply the required higher average output voltage than the open circuit battery voltage. It then controls the average voltage and current by sensing both and regulating with the correct Mosfet switches according to the profile selected (fast, slow) to change the PWM duty cycle.
Now the re-generative brake does a similar thing except the rear brake would be supplemented with dumping the motor energy rectified and regulated back into the battery. There are limits to battery current, just like fast accelerating and fast charging, age the battery faster, you might be able to replace the use of the rear meachanic brake with an electronic break, but also perhaps not without limits.
But let's think about the energy you want to use.
Ecap=1/2 C*V ^2 = 1/2 500F * 2.7^2 = 1822 Wh * efficiency of conversion.
Ebattery charger= 60?V * 5?A * 3?h = 900 Wh
So both methods would be very useful to incorporate Ecap and re-gen charging, but losses can be significant.