Yeah, sure it's further along. But these kinds of planes fly at 100-200mph.

But mach4 is at least 1000mph or more (depending on altitude). So while the envelope of feasibility might be doable at 100mph or 200mph to go from 100mph->1000mph requires 100x the amount of power. Going from 200mph to 1000mph requires 25x the amount of power.

So here's the rub: not only are your power requirements going up but also your total energy requirements are going up. This is why the Concorde stopped flying. We're too cheap to go fast. Using energy at 100x the rate to go 10x as fast means that your total energy budget has to somehow miraculously go up 10x and 10x more batteries could easily keep a plane from flying.

As battery tech gets better we might find it's possible to do really useful stuff with electric planes. But until really major breakthroughs happen we won't see electric cargo jets or electric-to-launch-orbit. It's not nay-saying that will prevent this but basic physics.

How could I have better put not trying to argue that it is significant to space flight?

The basic thought behind my comment was that people reading your comment might find electric airplanes interesting but not be aware of the progress being made.