Given the data and research that goes into these sorts of high dollar races, I suspect it wouldn't be very interesting. It would be a relatively simple calculation (that I cannot do and do not know all the variables for) to determine when the benefits of batteries clearly outweigh the benefits of combustion engines with quick and simple refuels. These teams know exactly how many laps they need to complete and the speed they need to do it in order to be competitive. They track the fuel and refuels and other pit stops very closely, so as soon as they can see they would benefit from batteries I'd expect almost the entire fleet to switch over. There will be almost no overlap between electric and combustion cars in races.

The only benefit combustion engines have is the current faster refuel and run time. Everything else about electric motors is far superior to combustion. If and when F1 can hot-swap battery packs efficiently, combustion engines will be dead in that sport.

No. The first few seasons of Formula E were such that, half way through the race you jumped out of one car and finished the race in a second car. Because your battery was dead. Electric does not have the capacity to compete with even F1's artificially limited gas tanks.

This is despite dramatically reduced performance design and slower tracks.

Formula E is so much more fun than F1 though, because it doesn't have all the BS drama that F1 has adopted to buoy viewership. They do have silly gimmicks though. Before a race, viewers vote on which driver they like the best, and that racer gets a boost they can use during the race!

Also they use tires that are basically road ready, so that's fun.

It's a regulations driven race. It would be hard or impossible to make any kind of fair rules and it would still end up a race about which manufacturer and driver(s) can find the best spots in the rules to focus on.

Outside of Formula or Nascar or other monocultures, that would be interesting, though.