Its important to be clear when you say AC motors have regen.
All AC motors are not created equal.
The AC induction motors on your table saw will not regen, and are made to run in syncronus with the 60HZ line frequency.
Hybrid cars use permanent magnet brushless AC motors.
The permanent magnets on the rotor of the brushless AC motors are natural generators whenever they are turning.
They are synchronous motors, so to speed them up or slow them down you change the 3 phase AC drive frequency.
Neutral
The 3 phase drive frequency needs to exactly match the voltage and phase of the 3 phase generated back EMF voltage for there to be no power going into or out of the spinning motor/generators.
Drive
To make the motor drive, you increase the frequency of the drive signal, so the drive signal leads the back EMF signal from the motor generator, and the voltage difference accelerates the rotor to try and catch up.
Regen
To get regen, you make the drive signal lag the back EMF signal and current flows back from the motor/generator into the batteries.
This type of motor has a high flat torque output curve, wide operating rpm range, and very good efficiency.
The prices of the variable speed drive controllers is coming down.
Kelly High Power Brushless DC Motor Controller
One last confusing point, Brushless AC motors(BLAC) and brushless DC motors (BLDC)are pretty much the same thing, as you cannot make a permanant magnet spin inside of coils without generating a rotating AC magnetic field.
When you have a brush motor, the copper commutator changes the DC to AC, so in practice there are no DC motors, they all run on AC internally.