Disclaimer - I am not a Roadster owner. Having said that I don't understand the lure of more range with respect this specific car.
Personally, as a Roadster owner, I don't think more range holds much appeal. My driving tends to be either well within the current pack's range (anywhere in the Puget Sound region) or far beyond it (
crazy trips to California). More range would make the Seattle-Ellensburg-Spokane drive easier, but that's a rare trip for us.
For folks who want to drive from San Francisco to LA non-stop, it may hold more appeal. When I drove from Seattle to Monterey for Teslive this summer, I found that stopping at the 70A HPC charging spots down I-5 made the drive quite pleasant, far less exhausting and probably much safer, than driving 400 miles at a stretch without a stop. I had WiFi at most stops and was able to work while charging. The car was always ready to go before I was.
Looking at the purpose and function of the Roadster, isn't performance the desired attribute? Can one (or would one want to) even sit in the roadster for 5-6 hours nonstop between LA-SF? To me it feels like Tesla is doing a magic trick - distracting with the 400mi talk - while behind the scenes/quietly working on the performance (i.e. acceleration) figures. Is it unreasonable to expect that 3.0 will have awesome/super car 0-60 #s with the new pack and that's the real news?
Better performance would require a new PEM and motor.
Dropping new cells into the same battery package format doesn't sound like it would take much engineering effort, although I'm sure it's more complicated than it sounds; it always is. They will also need to update the firmware, at the very least for a different charging profile and SOC calculation. Those sound doable for a tiny market, as a gesture of goodwill for the early supporters that made their current success possible, and a sign to Model S owners that they won't be abandoned when Model 3 become Tesla's flagship vehicle.
Designing a new PEM and motor sound like much more significant investments in engineering and manufacturing, things that seem wholly impractical for a tiny, and constantly shrinking, market.
The same holds true for Supercharger support. It would be great, but it would require a big investment in designing and manufacturing a new PEM, which I just can't see ever happening.