That's exactly what I'm hoping is NOT the case... taking a smaller battery and squeezing 20 more miles out of it hurts it's longevity in the long-term.
In fact, my suspicion is that they will be
55 kWh, mainly because all the other Model 3's have ratings of ~4.4 Miles/kWh.
Also the weight difference of only 50 pounds is another hint, since 11 kWh of batteries weighs 100 lbs (with an Energy Density of 247 Wh/kg)
I'm very curious to see the actual number the car uses:
If the Standard Plus has a 50 kWh battery it will take the most wear and be pushed the hardest, and have the shortest lifespan.
But if it does have a 62 kWh battery it will take the least wear, and have the greatest lifespan of all the Model 3's!