TEG

Well, depending on how they engineer the thing you may have reduced performance when the battery pack is run down. For instance note how the Fisker plans to have a paddle on the steering wheel to switch from "Stealth" mode to "Sport" mode which will fire up the ICE to add some more power to get the eMotor up to full output (apparently the battery pack is inadequate by itself). If you have an ICE big enough to fully power the vehicle then you are carrying a lot of weight around.

If you are willing to fire up the ICE more frequently then you can consider some benefits:

#1: Battery pack doesn't have to offer as much max power output because you can supplement from the ICE/generator when requested.
#2: The ICE doesn't necessarily have to be as big because you run it while the batteries can help so you get a power blend for a longer range than you would get from the pack alone. Eventually the pack will still run down so you would end up in a low power "limp" mode if the ICE/generator was too small to keep the pack from getting fully discharged.
#3: You can drain the batteries more slowly if the ICE/generator is helping so you may be able to get through the month with less range of pack cycling which could help the batteries last longer in the long term.

Imagine you had a weight & price target, and you could take two approaches.

Approach #1:
40 mile battery pack + 70HP ICE generator
The vehicles runs on 100% battery until near empty then the ICE kicks in until you get to a plug. (Trying to be like an EV but with an emergency generator that maintains close to full performance on fuel alone when the pack is spent)

Approach #2:
80 mile battery pack + 20HP ICE generator
The vehicle starts up the ICE much sooner. You could go perhaps 250 miles on "blended power" (extended 80 mile pack + ICE assist) before you run the battery pack down and experience reduced performance (limping to a plug)

Approach #1 would be better if what you wanted was < 40 mile daily commute and never start the ICE. Also if you had a pack that could stand up to daily full discharge / recharge.

Approach #2 would be better if you routinely drove more than 40 miles but less than 250 miles before plugging in. You could do a fairly long commute without ever running the pack all the way down which would likely give the battery pack a longer lifespan.

I hope you can see what I mean - driving habits and plug-in habits could dictate different designs.

If you are willing to use "blended power" (ICE generator + some pack capacity) together then there are a lot more options as to how you size and configure things.