I think K. Rool will still look larger than Donkey Kong, since he stands upright and wears a crown (which I doubt would be part of his normal hurtbox).
It's funny, because DK and Samus are very near the same height in Brawl, and some argue that we can't have K. Rool and Ridley because DK and Samus are already some of the tallest characters.
Don't get me wrong, I have no problems with both K.Rool and Ridley (I like these characters), but I just prefer them too be bosses rather than playable characters.
And if I had to choose one of them as playable, then I prefer Ridley over K.Rool
Because...
1. His body structure (his appearance) is more unique and interesting than K.Rool...
2. There's already 2 DK characters and only 1 Metroid character (not counting Zero Suit Samus), I rather want a new Metroid character...
3. I can see that Ridley's moveset is overall far more better and unique than K.Rool's
I'm honestly not sure what K.Rool can do if he was a playable, can he bring something new to the table?
How about moves based of his size and his status as 'king'? Well, we already got Dedede and Bowser which already does a pretty good job in this area...
Throwing Kremlings? Dedede already does that with Waddle Dees,
and throwing big Kremlings would just look silly... the only thing that I see him throw is Klap Traps... and that's about it...
However, if K.Rool was a boss, then this could work perfectly!
Using his body (size and weight) to attack? Both Bowser and Dedede does this already, and Bowser even has two moves (Flying Slam and Bowser Bomb)...
LOL, even Snorlax has more stuff to show than what K.Rool has
So if K.Rool will be added to Smash 4, then his moveset SHOULD be more or less based of how he works in DKC2. But I don't know...
He could do the stuff above, but I don't want him to turn into "just another clone"... that's why I have no problems with him being a boss...
If I want a Kremling, I would personally like to see Krusha as playable character, simply because his size is not a problem and a muscular crocodile with a brutal militarish moveset could work...
Just by looking at him in DK64 makes me think that he could actually work pretty well
Unfortunately I have to be realistic, he's not a popular character in DK series and I'm very annoyed by this
I'm sorry if I'm being negative, but this is my stupid opinion...
and sorry about my grammar, English is not my primary language