Tesla would have a huge risk with your strategy, @jhm: if the vast majority of customers opt to wait, the production lines would be idled while the new model awaits production. I think that the time between announcement and commencement of production has to be short, and further that there needs to be a step-up in price, to limit the impact on production and the regret of customers who receive the older model ("at least mine cost less").
I think that this is what we'll see for the AWD Model S release. While we few here on TMC know that it's well along and likely to be released this quarter, Tesla has been silent about a release date. I seriously doubt that people who have finalized their orders this month or next will be able to modify those orders to be AWD. Short lead time on announcement, step-up in price.
Yeah, I recognize that risk. In the case of higher density batteries, a modest price increase may be consistent with the objective of holding the price stable. For example, price the 100 kWh $6000 above the 85, the 70 $4000 above the 60, and offer a 50 $4000 below the 60. (Note a higher density 50 could get more miles per kWh than the 60, and it would give the impression 5 has Teslas are becoming more affordable.) Such a pricing scheme does no reason fundamentally increase the price of the Model S. In fact, on a per range basis, it would slightly decrease the price.
If this modest repricing was not enough to keep the factory running at full capacity, then at least two more options remain: divert more old version cars into the service loaner fleet and sell cars with a rebate. Either way, Tesla is absorbing the reduction in value due to discontinuation. I would prefer this to the rebate check idea discussed upstream. There is no need to give away apology checks to someone who purchased a car prior to the announcement of an upgrade, but as a practical matter a rebate offered to a post-announcement buyer may be needed to clear inventory. But it a pricing scheme like the above is in place the perhaps a modest rebate of $1000 or $2000 may be needed so close the sale. Again this would not be such a big price adjustment as to alter the basic resale value of older Ss.
On the other hand, an option like AWD is not likely to create much of a problem. The option will carry its own price and only a fraction of buyers would want it. I, for one, would not pay an incremental $2000 or wait an extra month for it, so I would happily take delivery earlier while others wait for an option that they more highly value than I.