I'm rather surprised that Pon & Con from KDL3 are set to make an appearance in this game. To be honest, nobody seems to have expected these two to appear in this game.
Honestly I never expected those two to ever appear again at all... I like them but I just considered them to be already forgotten along with Acro.
Then Acro was brought back in Planet Robobot, with the Nruff treatment (declassed from boss to regular enemy), and Pon & Con happend. Everything is possible with Kumazaki as director!
On a side note, in a different thread I said that the thing I wanted the most was a comeback of Adeleine.
It turns out that it's very likely that she's in Star Allies.
I have a theory, and it's not a random theory just based on assumptions, there are some big hints, not a solid proof but enough big hints that I think she has at least 80% of chance to be in the game, if not more.
Let's start from the beginning...
-Kirby Star Allies has those puzzle pictures that you can watch after collecting puzzle pieces in the levels.
-the Kirby 25th Anniversary twitter has reached 100.000 subscribers, and HAL made a special post with an artwork, claiming that the artwork was drawn by Adeleine and implying that every artwork in the twitter page was made by her as well.
-Some Famitsu scans contain a lot of informations but they are in Japanese... a Reddit user translated them and it turned out that the pictures in the gallery (those puzzle pictures) are made by "a famous creator".
Now, there is a screenshot of an incomplete picture that represents Kirby, Dedede and something else.
There is a square thing in the center, and an odd thing on the left, near Dedede's hand.
look at the screenshot and some examples: https://i.imgur.com/uJVCN2x.png
That thing seems to be similar to Paint Roller's face, and if it's true, then the "famous creator" is paint roller (but the picture is incomplete and it's hard to tell).
That thing also looks a lot like Dedede's hammer, and the square thing in the background may be both Paint Roller's canvas or Dedede's boxing ring.
In case it's Dedede's hammer/ring, and Paint Roller is not featured in the picture at all, the most likely possibility for the "famous creator" is to be Adeleine, since the artwork looks similar to the twitter arts and HAL said that those pictures are drawn by her.
The Dedede Ring/Hammer theory is more likely to be the correct one, since you can see Dedede's logo at the center of the ring, and Whispy in a corner, along with Kirby's classic look: this means that the picture represents Kirby's Dreamland 1 and to be more precise, its bosses... Paint Roller was introduced in Kirby's adventure so it can0t be part of the picture.
Probably each picture represent a different game.
If all of this is true, Adeleine has a role in this game, maybe not an important role story-wise, but an important role as representative of one of the game's core feature, along with confirming herself as the "art mascotte" of the Kirby series as a whole (with the twitter thing supporting this) and a recurring character (third time she had a role in a main Kirby game).
It's not confirmed yet, but it's possible that she's coming back to stay, no more minor cameos!