As said - check with your MCU in particular, but nowadays, most of them have Schmitt trigger inputs anyway, so the additional gate is useless.
As for debouncing, I'm not against what you did here, depends on the kind of input you use really. Since it seems to be designed for "digital inputs" as well, I'm not sure the RC filter would really be a benefit in this case. As for the clamping diodes, why not, but I would then add a series resistor *before* the diodes. Depending on your input signal, you may even want to add a TVS diode.
Point is - the extra gate is likely useless here, and more generally speaking, designing some kind of "universal" input like you seem to be doing here is IMHO not a very good idea. It's IMO a better approach to adapt it to the kind of input you'll really have to deal with. If you're using a mechanical switch, the extra clamping diodes are probably useless. OTOH, if the input can be connected to some kind of external signal through a connector, then better protection than what you did here would probably have to be considered.
As for pullups - leaving CMOS inputs floating is never a good idea. If nothing else, it will tend to draw unncessary current.
But if you get rid of the extra gate and enable internal pullups of the MCU, then the point is moot. No extra pullup needed, although depending again on your specific case, you may want to add an external, smaller value pullup (like 10k or lower) to avoid potential spurious state change due to external perturbation.