This actually reminds me when Banjo and Conker were in Diddy Kong Racing, as their games were supposed to come out the same year but had to be delayed. DKR's development was going well so they were put in the roster to make up for the delays. More importantly, they also did it to help players recognize them in future games when they finally did come out.
Worms is dang popular, and Yooka Laylee being in the new game is great as it will do just what Diddy Kong Racing did. Couple that with Playtonic inserting their own characters from their future projects into Yooka Laylee as NPCs and they'll surely get even more new fans who never followed the game's development to begin with excited for their newer projects.
All becoza Worms.