As an investor I don't want to see the S price come down ever
I would suspect the stock gains associated with having a very high profit margin would benefit my portfolio a lot more than a cost reduction when I am in the market for an S.
I also believe that the Model E will have a huge range of offerings: from bare-bones starting at $35k going all the way up to an "M3 Destroyer" in the $60-70k range. If you can't shell out for the S, the E will have you covered.
When the gross margin for the S gets to the point they want it... 30-40%? They could then reinvest in luxury upgrades and technology as battery prices fall rather than reducing the price. This would keep the S at the top for a very long time and keep investors very happy.