Geno hasn't been relevant for a very long time and has a skillset similar to a certain blue bomber that could probably use some fresh air. Krystal has been introduced as a damsel in distress who's claim to fame is using a weapon that she never even used for more than 10% of the game she appeared in.
Umm... the Ice Climbers haven't been "relevant" in a long time either. Heck, why even bring up the "relevant" thing anymore=??? Ness, Jigglypuff, the Ice Climbers, Mr. Game & Watch, Marth, Roy, Ike, Pit, R.O.B. and now even Captain Falcon are irrelevant outside of smash.
Geno wouldn't be anything like Mega Man. Having played every classic Mega Man game, I don't see where you are coming from. Geno's got a machine gun thing; Mega Man has a mega buster generic shooting gun.
Krystal, on the other hand, has a pretty awesome staff, and also is a psychic. Heck, I hate Krystal as a character, and I don't want her in smash, but she's at least important to her franchise.
Really, comparing what some of us have as "guilty pleasure" characters that we would see (like a Geno) is not a crime, especially to what people on GameFAQs expect to see character-wise (Andross' nephew had a noticeable fan base over there pre-Brawl). To simply compare them... shows that you haven't been to GameFAQs (which is a good thing).