Impa, understandably, is a bit of a controversial "wishlist" character moreso than a logical prediction. However, I absolutely must disagree in regards to Toad and Tingle. Tingle is definitely not scraping the bottom of the barrel - he's unique, re-occurring, has a quirky personality and has had three of his own games. I keep bringing up the spin-offs even though it's been ages since they were released, but the fact Tingle had spin-offs at all makes it pretty clear that Nintendo saw some big potential in him, not just as a character but as a face that would sell. Granted, the Western hatebase of Tingle sort of takes his chances down a notch or two; I guess if the Tingle games had seen release outside of Japan and Europe (Eurofag here) he'd at least have a little more support going for him from American fans. His spin-off games
are of importance though; there are characters in Smash who don't have much history to their name, whereas Tingle has the advantage of having both his own spin-off games
and a long-running series of cameos in the main Zelda series. Between that, his interesting playstyle and his potential for a unique moveset, I'd say he's not
'bottom of the barrel' at all.
As for Toad, it was neck and neck between him and Bowser Jr. for a while, but Toad won it out in the end. Yes, it was partly based on his age and long-running position in the Mario series, but it's also due to his popularity in Japan. I'll pull the links up for you in a bit if you'd like, but Toad was ranked 8th most popular video game character in a Japanese poll that took place in 2008, as well as one of the top 3 playable characters in a poll concerning peoples favourite racers in Mario Kart. And just like Tingle,
Toad has had a spinoff title of his own, called Wario's Woods. As for playstyle potential? Toad has plenty of it, being able to take reference from games spanning as wide as Mario 2, to Wario's Woods, all the way to the newest Mario platformers - and that's to say nothing of his unique attributes, being small and incredibly light, whilst also being fast, poor in the air yet able to carry characters and throw them around with the same prowess as Donkey Kong. I can't think of any other character with these kinds of unique stats and attributes.