Obrist...Tesla consists of a two-cylinder, 1.0-liter gasoline engine ... claimed to deliver fuel consumption of just 2.0 lt/100km (118 US mpg/141 mpg Imperial).
https://www.carscoops.com/2021/09/ob...a-into-a-phev/
At a guess I would say an economical series hybrid should ask you where you're going, GPS style (with saveable/selectable favorites), before you leave.
Then it's computer can work out just how much and where the ICE should come on.
ie:
Know that for eg: its a std commute to work where you will plug in to charge.
(saved to/selected from favorites)
Or that you are just nipping to your local cafe quickly (close) and there's no reason to come on at all.
The computer might even log these trip's to better learn just how much regen you will be getting and where you will be flooring it up a steep hill, etc.
ie: learn your normal routes.
Another issue with series hybrids is cold starts.
I would guess that, during a longer trip, it should come on often enough to avoid cooling down too much.
Coming on during most all accelerations to minimize amp draw from the battery (increasing it's lifespan), is probably the way to go.
In short: (What everyone is calling) A.I... for economy...
E.I!
But at the end of the day, only the driver really knows whats actually going to happen ahead of time...
So being able to press an on switch because you're about to race a Lambo or something is a necessity!
IMHO.