I'm new to DIY CNC, and I'm curious to know what one would do with all those inputs and outputs on the UC300eth?
Whatever you want. Inputs can be used with sensors, switches, pushbuttons, signals from servo drives, encoders, probes, MPG's,....
Outputs can activate relays, contactors, solenoids, LED's, .....

You can create your own M-Codes in UCCNC, which are written in C#. It doesn't have ladder, but you can write what they call macroloops, which are macros that run continuously in the background.

If you need full Fanuc macro B, I think your only option is Mach4 Industrial. But you can do more basic parametric programming in UCCNC and most others.
I have no use for parametric programming, doing everything I need in CAM.


You're not going to get a $10,000 control for $300. No hobby controls are perfect. UCCNC is relatively new to the market, and I expect it will be maturing for a few years still. But for me, it's headed in the direction that works best for me.