Certainly it is a niche market, and a great deal depends on infrastructure that only exists along narrow corridors. That's the other part of why I think Zero is unlikely to go all-in on a touring design this next year.
However, ignoring infrastructure for a moment I don't think it's that far off of being practical.
One way to look at is riding to charging ratios, or time spent on the bike vs time spent off the bike.
20 kWh bike is 2.3:1 at 70 mph, 4:1 at 50-55 mph.
Tesla Model S with a Supercharger (5x the power) is around 3:1 at 70 mph, 5:1 at 50-55 mph.
Another way to look at it is time to charge 100 miles.
20 kWh bike is 37 minutes at highway speeds, 30 minutes at 50-55 mph.
Tesla Model S is 28 minutes at highway speeds, 23 minutes at 50-55 mph.
I've only done a little bit of gas touring - a couple 100 mile and 200 mile trips - so I'll only speak to my experience as a non-Iron Butt rider. I liked to stop for around 10 minutes every 100 miles or so, re-fuel, shake out the limbs, decompress a bit then get back on the bike.
So comparable gas numbers for me are 9:1 ride to charge @ 70 mph, 12:1 at 50 mph .. and 10 minutes every 100 miles.
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The vast and overwhelming majority of the trips I take are in the 100-200 mile range. For many of these trips the 20 kWh bike would not need to stop to charge at all, or could spend 15-30 minutes charging mid-trip and be back on the road. A more complete charge could be obtained overnight or at dinner / activities, provided J1772 AC infrastructure was available.
This very much puts it in the ballpark of a gas bike, which would typically need to stop once, possibly twice to refuel on a similar trip. 0-10 minutes stopped with gas vs 0-30 minutes stopped with electric mid-trip is a trivial penalty.
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The real key will be finding batteries that can safely accept 2-3C charge rates with 15-20 kWh onboard. I think this will line up with settling on a fast charging infrastructure in several years time. Charging at a full 48 kW from CHAdeMO or J1772 Combo is 5.5:1 at 70 mph, 10:1 at 50-55 mph .. or 15 minutes for 100 miles on the highway, 12 minutes for 100 miles @ 50 mph.
This is very close to zero convenience penalty over gas for touring on very long trips, and possibly ahead on short trips. Again, much depends on infrastructure being rolled out.