Weak pull-up resistors are already built-in. If longer wires are used to connect signals to PoKeys device, additional external pull-ups (1 kOhm) are suggested. If internal pulse generator is used, there is a requirement for 470 Ohm pull-up resistors on step signal pins (see the manual on Pulse engine and Mach3).
The revision v1.2 should already have the pull-up on the probe input installed. However, this still needs some additional tests and until these are confirmed, we suggest adding an additional external pull-up.
As Max pointed out, most users won't be using sensors values at all, so there was no real necessity to support them directly. Since Mach4 can communicate with the PoIL diagram (created using PoBlocks and run in the device), one can read the sensors in PoBlocks and forward them to Mach3 via 'PoIL shared slots'.