"The question coming in mind is should I use some sort of filter or buffer in between keyboard and micro in order to satisfy No input should be a uC pin. "

Here the Murata ferrite as pointed out by Erik should help you ? In fact it is a good suggestion as I am on the verge of closing out the layout for a 30input / 12 output I/O pcb. The design has been put on hold till I locate a ferrite bead that can sourced locally.

Raghu