Worry about the "nobody cares enough" problem long before worrying about the "oh crap, too many people care" problem. User apathy, aka "not enough traction" kills far more startups than inability to scale. Pick the ecosystem with which your company will be most efficient and agile, and cross the scaling bridge if you come to it. We've rewritten substantially all parts of our codebase and key infrastructure 2 or 3 times in the last 8 years. You'll get the pleasure of doing the same iff you have users...

Bear in mind that developer experience and smarts count for more than anything else (if you don't have those yet, don't worry - they will come with time, patience, and effort).

That said, I would say that languages and technologies that help you achieve a more modular design will help you scale more. This makes it easier to tear things out and move them around so you can alter your architecture much more easily than you would otherwise. And of course efficiency (in terms of code performance) doesn't hurt either, but I wouldn't choose something on that alone. If you can have efficiency and modularity, so much the better!