The problem with the NIO EP9 record is that it's not even a street-legal supercar.
Somewhere I've seen someone pointing out that it beat the Pagani Zonda R, but if you're including street-illegal cars, that's not the car to beat
. The car to beat would be the Porsche 956, which set a 6:11.13 on the exact same circuit configuration as NIO's lap, in 1983.
Perhaps one day they'll create a race-series where you can swap out entire battery packs like a traditional refuelling pitstop at the moment, but that goes against the current design philosophy of integrating the batteries into the floorplan to keep the centre of gravity as low-down as possible and welding armour over the part of the chassis holding batteries to prevent damage and subsequent thermal runaway.
Well, Tesla's armor is bolted to the chassis, instead of welded, and they've designed it for 90 second battery swaps - it just turned out to be uneconomical to do those swaps, when their charging was fast enough for road car usage.
I wouldn't be surprised if you see someone doing an electric Garage 56 entry at Le Mans, probably in 2020 or so I'd guess. Maybe side-loading batteries?Edit:
Also, some of how I think a Garage 56 entry could work... Garage 56 is targeted to LMP2 pace. The winning LMP2 pitted 33 times over the 24 hours, and did 357 laps, so let's call stint length 10 laps here due to increases in pace for 2017. In a LMP2, a stint is 75 liters of fuel. Now, I'm going to guess that LMP2s are somewhere around 35% thermally efficient on average, and an electric would be about 90% thermally efficient, so you're looking at about 29.2 liters of gasoline equivalent.
One gallon of gasoline is 33.7 kWh, so you're looking at right about 260 kWh of battery required for a stint... but I'm not done yet.
At least with road cars, you're looking at about 1/2.4 (Smart ForTwo Electric) to 1/3.1 (Kia Soul) the energy used by an electric compared to the same non-hybrid gasoline vehicle on the US highway cycle, so that just dropped to somewhere between 84-110 kWh needed.
Then, consider that you can get the laptime in more efficient ways than brute power, especially in Garage 56, where huge parts of the rulebook are suspended. DRS (which will help a lot
on the Mulsanne), all sorts of low-drag techniques that the ACO forbids to keep the cars slower, torque vectoring, rear-wheel steering, and a bunch of other techniques are available. I wouldn't be surprised if a purpose-built Garage 56 entry could be done with 42 to 83 kWh of battery. I think battery swapping will still be necessary, because even 300 kWh charging is too slow, but still...