I'm an 80% kinda guy. BMWs BMS is a decade old compared to what's available on EVs being introduced today, and all of these newest cars – including the new BMW EVs – come with user-selectable charge management. The new BMWs even allow charge current selection (not just "reduced rate" like on the i3)
I believe that BMW was attempting to make the i3 ownership experience trouble-free when they decided to leave this out, and adding it in later would be an admission of their oversight, and potentially open them to liability – not to mention paying to update software on a lot of cars.
I hope my 120 Ah battery had better chemistry and lasts longer than the original 60 Ah models.
One complicating factor in assessing this is that 120 Ah batteries are used less (on average) than their 60 Ah counterparts. In other words, if the average daily distance driven is 40 miles, then the early batteries were using 50% of their capacity daily, where the 120 Ahs are only using a quarter of their capacity. That right there should account for the larger battery degrading at half the rate of original.
Of course the i3's generous buffer helps, but it's divided between the top and bottom of the pack, so 100% indicated is really 95% or so – nowhere near 80%.
Anyhow I'll continue to manage my 80-ish% charge manually, no biggie, I also don't sweat it if I occasionally charge to 100%. I hope this pays off as the car ages.