On a side note, one of the benefits of Tesla ownership is that you often get improvements in your car via OTA updates. Can add new featured from time to time.
On my 2017 X-75 I have received variable automatic windshield wipers, auto dimming headlights, improvement of 0-60 time from 6.0 to 4.9, faster opening/closing falcon wing doors, Extended Autopilot, and other updates since buying.
That battery thing is always going to get better, but current battery range of 310 is certainly sufficient for most owners. Very few will require more than that.
Current offering is very compelling, priced well and with good configurations available.
Elon said that sometime they will cease producing vehicles for private use all together. All production will go to an Uber Uber type of subscription agreement. Believe that will be the ultimate goal.
Imaging that even the specifications are already locked down for the upcoming Model Y. Perhaps after that Tesla can begin focusing on longer battery range.
Really few benefits to 400 mile range over currently available 310.