Watching footage such as the video bwh80 has shared, I get the impression it is somewhere in the middle, closer to Kazooie and Tooie in separate ways. Certainly in size, it is closer to Tooie; bosses are also closer to Tooie, it seems. Aesthetically, the names of places and bosses pop up on screen etc., which only happens in Tooie as well.
Overall I think it will be closer to Tooie. Tooie was a more ambitious game that attempted to do things that the team couldn't do first time round with Kazooie, and Yooka-Laylee is in the same situation. With today's technology, there are a lot more things that are possible; a greater array of things have become possible between then and now than between Kazooie and Tooie.
One area I think it'll be closer to Kazooie on are the collectables and number of moves. Tooie seemed to have a lot more 'fluff', but Yooka-Laylee seems to focus on necessary platforming mechanics only. There is no wall-grab ability, for example, but there is in Tooie.