The spacing of the Arduino pins (between 7 and 8) is a strange decision. But a big advantage of the Arduino is it's popularity. There are a lot of Arduino shields on the market.

The grblShield for example (https://www.synthetos.com/webstore/index.php/assembled-elect...). You just put it on top of your Arduino and you have a nice CNC setup.

But I'll keep an eye on the Teensy. Never heard of it, but it is looking nice!