You don't understand the Tesla order process. People waiting in line for Model 3 have not picked the exact details of their cars -- they do that right before the car is produced. If new stuff is announced, it's immediately available. So the only people who are pissed are those whose cars are in the assembly line.

In short, the delay between reservation and receiving the car is not an issue.

If they announced upgrades and that the new car was shipping in 2 months you would be at whatever current build was being deliver (sans any cosmetic changes they may request your input on). If the manufacturing lines are updated to add features as a baseline after you order but before your build, you will get whatever they are.