Assuming you already have a direct drive hub motor, the 'additional battery charging gear' usually weighs nothing. If you want to, you can design it to use the existing hardware. Mostly its a software thing.
BionX notably have for years had regenerating direct drive rear hub motors. They have four switched power levels and four switched regen levels, so the regen use and amounts are optional.
This is definitely true from an energy recapture perspective, but overlooks the even greater benefit of regenerative braking - almost zero physical brake wear & maintenance.
Absolutely. On my Nissan Leaf e-car the energy recovery is rather disappointing even in Eco mode despite its near one and half tons. But I do use the regen boosted Eco mode in all urban and suburban driving since the motor does all the routine braking, meaning the brake pads will almost last for ever. And it's relaxed one pedal driving.
Yes, that would be a benefit provided the hub motor/generator is on the front of the bike. It might be a bit of a handful to ride then though, especially when it decides to brake on the wet and ice.
There's no need to have the hub on the front. In fact, a rear hub has the potential to provide much stronger regen since you're able to mount the motor much more securely.
But most of the braking effort, and so brake wear, needs to be on the front wheel.
While that's certainly true when it comes to 'emergency' braking, the huge majority of braking is done with lots of time to prepare, e.g, slowing at junctions, hill descents, stop-start traffic, etc. This sort of braking doesn't require an abrupt speed reduction, so doesn't cause loading of the front wheel with braking force in the same manner. It is this sort of braking that regen is perfect for.
