I am considering adding a Model X to our family but I won’t make a decision until this onboard charger upgrade is either resolved or answered with an appropriate technical explanation.
Our S 100D has the 48A charger, providing around 10 KWhr of recharge per hour. Assuming we normally keep the car between 10-90% of charger (going lower or higher on a regular basis might have a long term affect on the battery), that means with 8 hours of charging, we can go from 10-90%, and in most cases we need less charging time (80% of charge would be around 240 miles of driving - for one day).
If you have a 72A charger, that would provide around 15 Whr of recharge per hour, reducing a "full" 80% recharge to around 5 hours. But if it's overnight, in most cases, you'll never notice the difference between a 48A or 72A charger - at least for overnight charging.
The only time this has an impact is when you are trying to charge during the day - and you can't reach a supercharger. And, to get the advantage of having a 72A charger, many chargers don't support that level of charging.
With our first Model S - I purchased the "dual charger" configuration - to get 80A of charging, because I was concerned about range anxiety. In the 5 years we've owned the car, I can recall only one time when we needed to charge that quickly - and that was after driving locally during the day, before heading out on a road trip that evening. Since there weren't any superchargers at that time, I had to leave with enough charge to get all the way to my destination, which had a public charger. Once the supercharger network was in place, haven't needed to charge at 80A.
When we ordered our S 100D, we no longer had range anxiety - and chose the 48A charger based on our experience - and likely won't drop $1900 to upgrade the charger, since we're not likely going to need it.
If this is the only reason why you're delaying a purchase of a Model X - then make some estimates of how much charging you are going to need - and where - and I suspect you'll find that whatever charger comes standard will be enough.