It's a bit more complicated that that. Even if an element is somewhat abundant but evenly distributed in the earth's crust, then it's difficult to mine. It's only practical to mine something if it's concentrated in some areas. E.g. gold is rare but you can find it in macroscopic flecks or clumps that are concentrated in certain areas. If gold were not concentrated like that but was instead uniformly distributed in the crust, there'd be no economical way to mine it.
That said, it looks like indium is concentrated somewhere: in zinc ores. So large scale production may be possible.