First of all, as of this writing, I feel the need to reiterate that this is just a theory, but if you read carefully and follow my logic I think you will see why I took the time to write about this.
What are Action Packs?
Action Packs are this year's Adventure/Battle Packs. Each Action Pack contains 1 SuperCharger, 1 Vehicle, and 1 Trophy.
For example, the Sea Action Pack contains Deep Dive Gill Grunt, the Reef Ripper, and the Sea Trophy. The Reef Ripper is Gill Grunt's Signature Vehicle so he will be able to supercharge it. The Reef Ripper is also a Sea Vehicle so it will be able to participate in all the races that the Sea Trophy unlocks.
I tried to cover everything the Sea Trophy unlocks in this video:
But I believe I overlooked one detail that plays a big part in my theory.
SuperCharged Challenges and Trophies
As I mentioned above, each Action Pack comes with a SuperCharger and their Signature Vehicle.
Combining these two figures on the Portal will not only supercharge the Vehicle, but it will allow you to play their SuperCharged Challenge.
As I was analyzing the SuperCharged Challenges this week, I noticed that they all but two take place on one of the six race tracks that are available to everyone when you get the game.
The two outlying Challenges belong to Deep Dive Gill Grunt and Astroblast. These are the two characters that are only found in Actions Packs.
As it turns out, you actually need the appropriate Trophy to unlock the track that their SuperCharged Challenge takes place on. Without the Trophy you won't be able to access their Challenge.
Not Sold Separately
With all that in mind, this leads me to believe that Deep Dive Gill Grunt, Astroblast, and their Signature Vehicles will never be sold separately. They are too closely tied to the Trophies.
We already know that Donkey Kong, Bowser, and their Signature Vehicles are exclusive to the Starter Packs because they need to be tied to specific consoles. So this association with the Action Packs does not surprise me.
We know what to expect in Waves 1-3. This lineup does not include the Land Action Pack so that has been a big question up to this point.
If my theory holds true and the Action Pack figures are not sold without the Trophies then there's only one option.
After Wave 3 releases there will only be one unreleased Land Vehicle.