I really liked that you got to control Banjo and Kazooie, a transformation and Mumbo in Tooie. Should transformations and/or another character to control be in Project Ukulele? Personally yes!
I think the ability to control different characters or to transform in some situations is an important gameplay mechanic in the Banjo-Kazooie series and also in the Donkey Kong series, so in my opinion its a must to have this feature in Project Ukulele.