DK's overall representation in Smash has been patchy. Roster-wise, Ultimate gave it a much-need boost with K Rool. The series now has a really diverse set of fighters, despite there only being three of them: a hard-hitting, heavyweight gorilla; a nimble chimpanzee and an obese, weapon-wielding crocodile king. Compare this, say, with Zelda, which has twice the number of reps but has three of the same character. Or Fire Emblem and its overabundance of swords. Despite DK's diversity in just three characters, however, it needs a fourth to be truly complete. As people have been saying, this is Dixie - a character whose been relevant throughout the series' history, contrasting with K Rool whose been absent in recent games. While Dixie is often suggested as an echo, this really wouldn't work for her. It'd be much better if she was a semi-clone like Isabelle, with a basis in Diddy but a DK-like recovery (helicopter hair rather than arms) and down special (hair slapping the floor). Her main distinguishing feature would of course be her hair, which is why an echo would be insufficient. Apart from Dixie, there are no other DK characters who feel essential. Cranky and Funky would be the realistic next choices, but they'd be more like a cherry on top if we ever got them.
While roster-wise the DK series is almost complete, the same can't be said for it's stage selection. The main issue is that they're very generic and essentially boil down to two themes. Much as Metroid has an overabundance of lava/acid levels in Smash, DK has too many which are either generic jungle scenes or rapid-flowing water. While there's some similarities to DK Country levels, they don't feel like they're based on anything in particular. The few exceptions are Rumble Falls (another rapid-flowing water level, and one which no one likes) and Jungle Hijinx. But neither of these levels are present in Ultimate, meaning the only DK stage which feels truly unique is the much-hated 75m. The DK series therefore really needs a new stage in Ultimate that doesn't fall into these cliches and actually feels unique. While I've seen people suggest Gangplank Galleon, we already have a pirate ship stage (two, if you count Paper Mario) and I'd rather not all of the new DK content in Ultimate focus around K Rool. It'd be better if it was based on a level from Tropical Freeze. The game has plenty of ice levels which could be turned into unique stages as well as stuff like Grassland Groove or Scorch n' Torch. All this is supposing that we actually do get more stages in Ultimate, though.
If DK's stage selection is lackluster, then so is the music selection. There's far too many remixes of DK Island Swing/Jungle Japes/Jungle Hijinx/Whatever it's actually called, and not much else. And don't get me started on what they did to the DK rap. Thankfully, Ultimate looks like it's remedying this somewhat. The new Gangplank Galleon remix is fantastic, as is what we've heard of Bonus Room Blitz. However, both of these are tracks which have already been remixed in Brawl (I think Bonus Room Blitz was technically just the map theme, but close enough). I really hope they branch out more with the remaining remixes in Ultimate. Not all the tracks have to be remixed though: Tropical Freeze's OST is perfect so could just be ripped straight from the game.
In other aspects, DK representation seems to be slightly improving. The series has finally got an Assist Trophy with Klaptrap and will hopefully get a boss or two in Spirits (probably Tiki Tong or Lord Frederik). Still, some of these additions took a while to come.
Overall:
+ The DK series is finally getting more love in Ultimate, mostly in the form of K Rool
+ The roster is almost complete ... almost
- ... but it won't be complete until we get Dixie
- The stage selection is largely generic
- The music selection is limited, focusing on a narrow set of tunes
Overall DK representation probably gets a 5.5/10