The person probably just has something against the "cut" characters in the roster and was a Dr.Mario main in Melee.
And seriously? Duck Hunt Dog? Not happening.
Well, not even that.
Dark Pit was already confirmed for a non-player role considering his reveal was casually passed over. If he was indeed playable, he would of been confirmed as so ASAP via the Palutena trailer as a bonus of sorts, like how Lucina was treated in the Robin trailer. Clones are piss easy to make, especially one that is a blatant color swap, so no there shouldn't of been any development problems causing a last minute switch out.
Also, there are Polar Bears in Smash Run, which consist of enemies based around stages or characters, the only exception is Subspace Emissary. Which should mean that Ice Climbers in some capacity is a real factor, whether it's a stage based on Ice Climber or the Ice Climbers themselves show up, the latter being more likely considering they've already appeared in past games.
There's also the subjective factor of limits on franchises, in this case the 7 Mario characters somewhat pushing the statements about trying to be equal with the varies franchises and not trying to oversaturate a particular franchise (i.e. too many Mario or Pokemon characters).