ChadS
Last tank of gas: March 2009
Get an invite somehow to the Model 3 reveal event next March and don't bother to look at the reveal itself; queue up where they'll take reservations right after the reveal.
This was @bonnie's MO for the X.
Yeah, that was funny. I had just met Bonnie at that event IRL, and a few of us were hanging around (and hanging, and hanging, as the event started late as usual) and the Model X came out, and everybody oohed and aahed, and Musk got out to talk about it, and I went to lean over to point out something Bonnie would think significant...but she was gone. Poof. When I saw her later, boy did she have a big grin.
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Every MS owner should get a preferred spot. WE made this happen, so we should get the option lest say for 48 hours or so to reserve first.
When the S came out, Roadster owners (as of a certain date) that made a Signature reservation got put to the front of the Signature queue no matter when they made the reservation (I didn't confirm mine until the last possible moment - July 31 2012, I think it was - but I got Sig #112 in Sept 2012). We also got a discount!
Of course, this only applied if we bought a Signature edition Model S (which was overpriced, though not by as much as the discount). And Tesla's situation is quite different now; I don't expect them to do the same thing. They no longer need customers they trust to go through with their cash-only purchase to go first (or even to just fill out the Sig quota). They no longer need existing customers to take a risk on a car that hadn't been reviewed and most expected to be kinda sucky. While I've talked to many, many Model S owners, I've talked to a LOT more people that are excited to become Tesla owners when the Model S is available.
It would be very nice for Tesla to do something for existing owners, and I hope they do something. But I expect it to be pretty small. Letting existing owners have first crack in some way still might be a good idea - and perhaps the method you suggest is a good one, though people on vacation and such will complain - but in any event, I will bet there is no discount this time!