Well, Marth and Roy are both Nintendo's, and they can do whatever they want to their own characters. Plus Marth and Roy got a game on Wii, it's OK for them joining the SSB series.
Remember NamcoXCapcom? Klonoa's moveset is inspired by "Klonoa Heroes", a game which wasn't released outside Japan. If Klonoa have a moveset similar to NXC in SSB4, that would be strange to western gamers. In the other games, like the latest game - DtP remake, Klonoa's relatively powerless and relies on Hwepoe/Lolo, and how could a "non-combatant" be fit in SSB4?
PAC-MAN's appearance doesn't make me interested, too. I think he's more suitable for other games, like Mario Kart (And he's already playable in the arcade version). However, what Klonoa really needs now is a new game, or porting/remaking. And we have to finish some fan projects first, so we can gather more people to help us.
BTW, does anyone knows what's new in SSB4? Will it be enough to promote the sale of Wii U? I guess the SSB4 team won't get budget cut for the game will be also released on 2/3DS.
One more thing: Did Klonoa used the power given by king of sorrow in Dream Traveller of Noctis Sol?