I haven't even decided whether I want the 300 mile pack or the 230 mile pack yet.
I am anticipating a huge price premium for that extra 70 miles. I am super excited to just know the pricing for the 3 battery options.
Here is a baseless guess for illustration:
The 160 mile pack: $9000, the 230 mile pack: $14000, the 300 mile pack: $22000
I will make a bunch of spreadsheets and min/max the crap out of it. The value of those extra 70 miles entirely depends on the availability of level 3 charging on the path to where I want to go ( however if there was a destination that was 231-299 miles from home that I wanted to drive a significant number of times that would tilt the calculation dramatically - regardless of the charging. )
Its quite possible I will start with the 230 mile pack but will want to upgrade to the 300 before 7 years are up.
In order to make money on the deal Tesla needs to guess the price the battery you want will be in 7 years and the time value of money and blah blah.
To entice me they will have to build into any deal some way to let me apply the money to whatever battery I want.
If I start with the 230 mile battery, and give them X dollars for my anticipated replacement in 7 years, but I decide I want to upgrade to the 300 battery instead, I will want to apply the money to that instead. If I give them $5000 for my 7 year away 230 mile battery - but after 3 years I want to apply it to the 300 mile battery that costs $10000 at that time, how much more will I have to pay? Will they only discount it $5000 giving me no appreciation on my money? That sucks for me.
If after 5 years, my 230 mile battery is down to 200 miles, but I really need a minimum of 210+ to optimize a common route, and I want to upgrade early what happens?
Since they have better information than me ( about what the batteries will cost 7 years down the road ), and I think they are pretty smart, I am pretty sure they will structure the deal so that it is good for them no matter what I choose.
I would have to see a bunch of very detailed formulas to let me explore all those scenarios.
If I can't convince myself that they are giving away some advantage in every scenario I care about just to lock me in, I won't do it.
So right now, I would say the chances are very slim that I would go for any kind of future battery deal on the model S.