Hey guys, I realised two different things earlier:
1. The music played in 'Swept Out to Sea' in Rainbow Curse is a calm version of Kine's theme.
2. Similarly to the theory of a new game featuring Dark Matter hypothesized by
Tortilla Noggin
a while back, these hints can also point out a Kirby 64 remake elaborated on below.
As I was saying, the hints for a 64 remake include:
Shadow Dedede: His 2nd phase having very similar attacks to Dark Matter-possessed Dedede (stomach firing orbs) which appears in Dream Land 3 and K64.
Meta Knight not appearing in recent titles: Although at the time of the Dark Matter trilogy MK was not as popular, one can't help but notice that his absences in Triple Deluxe and Rainbow Curse outside of cameos can be related to the trilogy and the absence of MK.
A Waddle Dee being a main character: As we know, a Waddle Dee helped Kirby and co. in 64. This can easily be related to Bandana Dee being a popular character in recent Kirby titles. This relates to my next point...
Bandana Dee acting very alike to Adeleine: In Triple Deluxe, BDee gives the player food items from the background. Adeleine does the same in 64, although she paints them.
Ribbon and Elline: They have similar back stories (fleeing their home area due to possession of friends, although this is unknown at the beginning of 64) and they are themselves very similar, being small fairy(-esque) female characters.
Final Boss: The final bosses of 64 and Rainbow Curse are similar, being cycloptic beasts that possess the friend of the fairy, and are fought in a shooter style battle.
This may be grasping at straws a bit, but it kinda makes sense.