I had the software updated on my 2017 leaf on 10/2/18. At that time I had the leaf for just under 18 months with 10,181 miles on the odometer.
Before the update SOH 88% , HX 82.43
After update SOH 93.64,% HX 82.79
A day later on 10/3/18 after 100% charge and a 70 mile drive
SOH 95.13, HX 83.4
On 10/20/18 SOH 93.34, HX 80.01 mileage 10,710
What I have noticed is that SOH does not fluctuate as much as it did before the upgrade. Before update, the SOH would change as much as 2% after a full charge and several longer drives. Other than the first day after the update, the variation is is less than 0.5% day to day. The SOH has stayed reasonably constant, and surprisingly the value of HX has seen a small steady decline.
I am not sure what all of this means, but it appears that battery degradation may not be that much better than before the software update.