Not all trips use I-80. Those trips using different routes than I-80 may not have the charging infrastructure.
Indeed - not all trips use Interstate highways, period. If you're touring, you mostly want to avoid them. We've gone for days and never hit an Interstate or major city, and we do it at least once a year or so. Of the 3K miles we drove on vacation, I'd say 2/3 or more were off-Interstate, and I wish it had been more. Thank God for gasoline.
Absolutely... I like to get off the beaten path as well. Many of those routes are still do-able today... As long as you can get *near* the beaten path every few hours. There are Superchargers being installed away from interstates now as well. Lake Geneva is one example in my area.
Getting up to Sidnaw is still a bit of a challenge. That's why you won't hear me telling Ed he needs to get a Tesla. Coming from his side of the lake, it's 170 miles to the Gaylord Supercharger and then 293 miles to Sidnaw. Plenty workable in the summer, but honestly downright dangerous in the depths of winter. When the Mackinaw City Supercharger opens up, it'll be much more reasonable - One leg of 230 miles, one leg of 240. When the Tesla Cybertruck comes out, the long-range version of that will have no trouble at all. (It's much easier from this side of the lake, where a quick stop at the Green Bay supercharger would be more than enough in any weather.)
I've always thought that it'd be really fun to travel the old Route 66 (as close as you can, anyway) out to the west coast, then the PCH and other roads up the coast, then back via US 2. The 66 portion is easy, since the corridor served by 66 is now served by I-55, I-44, and I-40 so the Superchargers are never far away. The PCH portion might be a little dicey between Daly City and Eureka (315 miles), though with that area's normal mild weather and the fact that you wouldn't be going interstate speeds should make that possible as well. I was actually surprised at how much of US 2 will be possible soon, with a Supercharger already installed at Leavenworth, WA and more planned... But once you're past Shelby, MT there's a gap until Great Falls, MT.
But, as time goes on and Teslas become more widespread, there'll be enough demand to justify Superchargers in more and more out-of-the-way places. I don't see this as a hindrance to EV adoption in the long term.