A number of people in the K. Rool Discord were looking at Google Trends and comparing his and other characters' results to make sure we weren't forcing Nintendo to go out of business by adding such an irrelevant dead villain to Smash.
Here are some of their findings. K. Rool is represented by the blue line, while the other character has the red line. The two big spikes you see near the end of K. Rool's line are in April 2015, when the Smash ballot launched, and in July 2015, when K. Rool's costume was revealed.
Of note, this is how Google describes the values in the Y axis:
Numbers represent search interest relative to the highest point on the chart for the given region and time. A value of 100 is the peak popularity for the term. A value of 50 means that the term is half as popular. A score of 0 means there was not enough data for this term.
K. Rool and Dixie:
K. Rool and Geno:
K. Rool and Ashley:
K. Rool and Elma:
K. Rool and Isaac:
K. Rool and Lloyd Irving:
The users tried doing other searches as well, but they turned out to be far more difficult to decipher. A search with Bayonetta, for example, comes up with results for both the character and her games. And most Mario characters and enemies beat K. Rool handily, though that's far from a surprise given it's, y'know, Mario.
Anyhow, read into this what you will. My take is, there might have been "silent majorities" investigating other characters on...Yahoo or Bing, but on Google, K. Rool was right up there with the best of them as far as characters people were curious about at a time when it mattered most for this game.