Let's say you want to go from SF to Seattle, a distance of about 800 miles. If you had a typical high-speed maglev train (250 mph), the trip would take about 3 hours. On an airplane, the actual transit would take a little under 2 hours, so if you get to the airport an hour early that's 3 hours total. (Personally I never show up to the airport more than 20 minutes early for domestic flights.) So for any trip longer than that, airplanes beat even high-speed maglev trains on speed. Of course there are factors besides raw speed to consider, like comfort and cost, but speed is an important one.
The bigger your country is, the more the fixed-cost of airline security is amortized over the distance traveled. If you don't have to travel very far, trains make sense. In Japan the population density is 10x higher than in the US, so trips tend to be much shorter. In the US, which is very spread out comparatively speaking, planes are much more compelling. So US trains need to either be really fast, or really cheap and comfortable, to be worth it.
The fastest maglev trains can go quite a bit faster than 250mph, by the way. For example Japan is constructing its "L0 series" which will have a top speed of around 375mph, and at this point you do compete with planes. Building one of these seems a lot more realistic than anything Hyperloop, but it's not like these superfast maglevs are anything conventional either, so I don't see the harm in experimenting with fun tech like vacuum-sealing the train.
Electric planes will not only be much cheaper to they will also be much more quiet and thus can potentially be operate in more places closer to where people need.
A major investment into a that technology seem a far better bet then trains at this point.
It's impossible for electric planes to be cheaper than electric rail - everything about a plane is harder to achieve, the size will be smaller (since it also needs to lift off the ground, not just drive), safety is a much bigger concern (leading to much more time for boarding procedures). The only advantage air travel has is that it doesn't require real-estate.
Instead, electric planes still need decades of engineering work, and what we know for sure is that they will be less efficient than kerosene planes, as there is no type of battery even plausible today that could achieve anywhere near the energy density of gasoline (in Wh/kg, not Wh/l as is sometimes shown).
