Electronic – Zener Diode for overvoltage protection

Assuming you're trying to protect an input (the outside world connects to the LDO input).. it does not provide protection against input voltages below ground. Absolute maximum input voltage is -0.3V.

It might work with a series Schottky diode, say for +/-30V inputs, but you'd have to evaluate whether the few hundred mV loss in voltage was acceptable for normal inputs (what your \$V_{IH}\$ is vs. \$V_{OH}\$) . I don't see where thermal protection would ever come into play, either as an input or as an output. If you exceed the 30V abs. max. input voltage, the part may fail.

You're going to need something like a capacitor in series with a resistor loading the output to keep it from oscillating. That will slow down the response considerably (you may want to add a load resistor to ground as well) and the capacitor could conceivably damage the GPIO under some conditions without a series resistor (if Vdd gets crowbarred).

Once you look at one diode, LDO, 3 resistors and a ceramic capacitor per input, it doesn't look quite as clean.

Something vital to remember when powering current-hungry devices on the bus cable, is that ground lift quickly becomes a problem, i.e. the DQ-GND voltage diff decreases since GND is lifted by the 24V loads.

If using a CAT5 cable, this can be mitigated by using multiple wires for GND. But with several 100's of mA in the return wire, I'm not sure that will be enough.

A local example: lighting up a 20mA LED with a DS2408 at the far end of my ~80m home network was enough to render the whole net unusable, power cycling it was the only way to get it back. When using three GND leads instead of one (in the CAT5), it works like a charm. Not sure about the rest of the load on the net, but it's some 20+ DS18B20 and a few DS2406's, nothing fancy.

(Sorry, don't have enough reputation to comment, so using Answer even if it is not an Answer...)