Are there any gas stations? Once electric cars become a relevant part of our economy, I don't think it will require a lot of effort (relatively to that scale) to have as many fast chargers as gas stations. Granted, in some areas it will happen sooner than in others, perhaps we are talking about 7 - 20 years for a complete coverage, depending for example on political determination.
I'm 63 years old. Not sure I'll still be driving in 20 years. I do think it will happen. I just don't think these rural areas, with long driving distances, will be early-adopter areas, and so I think fast charging will be slow to come. There might be a public fast charger between here and Seattle, but probably not between here and Revelstoke, B.C. very soon.
Not sure if you would consider the current 300 mile battery "affordable", but I could imagine a 400 mile battery in 3-4 years and a 500 mile battery (it seems those highways aren't high speed) in 5-7 years. So if you buy a 300 mile battery soon, your next upgrade/replacement might be 500 miles (at perhaps a lower cost additionally).
I would pay Model-S battery prices extrapolated out to a 500-mile battery. But I don't expect that to be available at current battery prices because of low demand. The routes I take up to Canada have some 65-mph roads in the US and some 110-kph roads in Canada. So fairly high-speed, yes.
But I am not aware of any OEM car maker offering any upgrade options after the sale on any car, other than safety recalls. IOW I would not count on being able to upgrade a first-gen Model S to a larger battery pack.
Anyway, as long as the S cannot make my trips up to Canada, I don't need another EV. My Roadster is all the EV I need around and near town, out to a 100-mile radius. I'll buy another EV when it can make my summer road trip, or when I cannot get in and out of my Roadster any more. It does take some contortion, and I'm starting to develop some arthritis.