Despite DC's popularity, Conan is probably not going to make his way into the ballot for a few reasons:
-DC is not known as a game series, so Conan really hasn't made his niche in the gaming realm enough for others to recognize him
-There really isn't much Conan has to offer for Smash. His gadgets aren't very fitting to the game either
-This event is mainly for fanservice. In all honesty, not many people are going to be excited seeing some random anime character appear on a roster--especially when there are loads of other characters with much more potential (Ice Climbers, Snake, etc.)
...and while Pokemon is a TV series, it's also a well recognized game series.
These are the main problems. Barely anyone has ever heard of games like Detective Conan: The Mirage of Remembrance or Detective Conan: Legacy of the British Empire (I pulled these from the wiki by the way because I've never heard of them either).
As for "Why should this character become a fighter?" the only justification is probably his gadgets ("crime-fighting techniques" isn't fitting for a game like Smash). You could justify his soccer skills, but it's still a relatively weak argument.
Conan is a bit of an anomaly compared to the other Smash characters.
And to be frank, he's probably not going to make it in.