I think Dixie Kong would be a great female character to add to Super Smash Bros. Ultimate for the Nintendo Switch.
My reasons are that she's a main Donkey Kong Country cast member and the DKC games are pretty big. In particular, she was a part of two of the most acclaimed DKC games in the series, those being Donkey Kong Country 2: Diddy's Kong Quest and Donkey Kong Country: Tropical Freeze. She even had her own game, Donkey Kong Country 3: Dixie's Double Trouble!, though that one tends to fly under the radar.
She's also one of the biggest recurring playable Nintendo female characters not in Smash yet. Toadette is in a similar boat, having been promoted to playable in both New Super Mario Bros. U Deluxe and Super Mario Maker 2. Either would be a great addition, and hopefully Dixie makes it in. Regardless, though, Dixie has a similar body type to another playable character currently in Smash, which leads to my last point.
Finally, while she would need more work than an Echo Fighter, she would not need to be completely unique and thus could have a lesser workload than a completely unique fighter, meaning the Smash team wouldn't have to work QUITE as hard when implementing her into the game. If you look at the reasoning Sakurai gave for Wolf's inclusion back in Super Smash Bros. Brawl, it's a similar proposition. Diddy Kong could inform a few of Dixie's moves while the rest would be unique, most likely relying on her classic ponytail that allows her to float.
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There. That wasn't hard, right? Notice how I never said she was the "most deserving" "over" other characters a single time?