GeoTheBacon here. So I went to do a little bit of digging; for sharp eyes individuals, you would have noticed that the there are multiple similarities between Master Boy and Missus Radiant. For those who didn't let me list them out for you;
1) They are both Link 2 monsters that can be summoned by 2 monster of their own attribute.
2)Their link markers both points in the same direction diagonally down left and right.
3)Their attack is 1400
4)They increase the attack and defense of their own attribute by 500 and reduce their opposing attribute by 400 attack and defense.
5)They both retrieve a monster of their attribute from the graveyard should they be destroyed by battle or card effect.
6)They both have cards that are almost like a younger version of them that was first release during the year 1999, in Vol. 6. ( Fun Fact Yu-Gi-Oh! The manga was first serialized in 1996 )
From point 6 we can conclude that there will most probably be 4 other generic link 2 for each of the other attribute to form a grand total of 6 of them. (I guess this may be paying homage to the older cards of Yu-Gi-Oh!).
The only difference of the older cards and this new Link monsters, effect-wise the link monster also change the defense and not just the attack and have the ability to retrieve cards from the graveyards.
Lets go through the ones we already know.
First off, EARTH
Milus Radiant And Missus Radiant
From the artwork, we can see this little feral (teenage?) puppy has grown up into a majestic beast that emits a calm aura, guess 17 years can really change someone's personality huh?
It's newer version's name Missus is used as a form of address of someone's wife, I guess marrying and settling down makes one calmer? I wonder who is Mister Radiant (LOL).
Next we have WATER
Star Boy and Master Boy
Looks who grew a dandy mustache, and now owns a fancy top hat, and a sweet monocle. Guess this little boy was successful in life for the past 17 years huh?
And now our prediction for the remaining 4 cards that should be getting a grown-up version of them as link monsters. (this 4 was chosen as they share similar effects and was released in the same booster pack)
First off WIND
Maybe it became a QueenFly? or Maybe it gets a cooler blade?
Next up FIRE
Little Chimera would have grown into a Big Chimera by now wouldn't it?
And Next Light
Hoshiningen, roughly translated into Star Human. or it's Japanese name SuperStar. Maybe by now he is more of a human than a star? or maybe he could become HYPER MEGA ULTRA star?
By now she should have become a very accomplished witch, or maybe she just became a Old Witch.
This are all mere speculations, only time and Konami knows whether this remaining 4 cards will get the same treatment or not.