Grbl is unlikely to have a complex pendant. It currently has three pendant like functions.
- Cycle Start
- Grbl Reset
There is a connector on the X-Controller to access those and we plan to "exploit" that in the future. These features are also accessible via software and can be very useful. Feedhold is actually faster than an E-stop because of capacitance in the power supply. E-Stop is safer in the true emergency.
Grbl Reset is an advanced feature that many people don't understand. If you feedhold a job because a bit broke, you can clear the planner and restart a job a little before where the bit broke. The machine will not loose it's place between jobs.
The way to do a full featured pendant is through the Gcode sender (Easel, Chilipeppr, UGS). A simple one could be made with an Arduino Leonardo as a keystroke sender. Chilipeppr has an awesome one using the Shuttle XPress.