While I agree, the "too recent" argument is subverted a lot more in Smash than you think. And some characters suggested for DLC would be way too recent; the Inklings, for example, being suggested in a fashion not unlike :meleeroy:.
And of course, characters that defy the too recent argument:
Greninja was based off concept art, and Robin's game was barely two years old.
I'm not defending Shovel Knight, mind you, but I'm just pointing out the small holes in the argument.
Shovel Knight is going to remain a popular choice despite his unlikelihood. But at the very least, unlike the blatant idiocy of Shrek and Goku, Shovel Knight actually makes sense.