I guess the fact that I have never used a VTT is showing! My concern would be if I purchased the "mini" don't I also get the stats for it? How does it function without the stats? And why would I have the stats without the mini?
I know lots of others have responded, but here is an actual VTT example that might inform the conversation.
On Roll20, I have access to what is in the SRD. If I pull out a goblin onto the tabletop, it is going to generate a small round token with text that says "Goblin" on it. But I now have a basic representation of the monster on the tabletop.
If I want something more detailed, I can buy the 5e Monster Manual. It has all the stats, and there are included tokens with the art from the MM attached to each monster that I can use on the tabletop. So, I have not only the goblin stat blocks, but I have the official Roll20/WotC Token for the goblin.
Roll20 also operates a marketplace where artists sell their products. In this marketplace are lots of other goblin images for sale. Some are other versions of tokens, some are top down images that more accurately feel more like minis, some are isometric or 2d versions. Maybe I'm looking for specific types of goblins, with shortbows instead of swords, or a wizard, or with a twirly mustache, or a specific art style. None have stat blocks attached, and I can buy them whether I own any specific game content on the platform.
If I purchase any of these options, I can open my game, open the official Goblin monster, and replace the official Token with whatever art I have purchased. Or, I can put 20 different images of goblins I have purchased onto the tabletop, and associate the stats with that token.
I could also pull an ogre out of the monster manual, but assign it a goblin image I've purchased, if I want to.
Ultimately, it is highly modular. As DM, I have complete control. But I am limited by what I have unlocked (or uploaded myself, as I can add my own images as well into the art library). So, I could run with the stock Goblin token, or swap out to create an entire cast of characters.
Applying all of this to the WotC 3D tabletop, it could be a few different ways they provide this. Maybe there is a default single goblin model you get if you are only using the free Basic Rules/SRD content (if they even offer that as a playable tier on the VTT). Or maybe they just have a general humanoid model (think crash test dummy) or go with a text labeled poker chip for anything you haven't purchased. You could still play, but it isn't as pretty as if you buy the MM and unlock the standard models. And there could be even cooler skins for those standard models that you can purchase, allowing your basic MM goblin to look like a wizard, or swap out weapons, or have a funny mustache, or add custom animations.
This all feels like what most VTT's are already doing, just with a slightly different twist because of the 3D nature of the platform.
I'd guess that as far as stats go, if you try to purchase a model of something you haven't unlocked (either through the free/SRD/Basic Rules tier, or through a book purchase) they would prompt you to buy the stats (I mean, to me that would make good business sense to help people opt in to buying more content). But it might not be required - they might also be fine if you want to use the model of the minotaur you just purchased as the art for the goblin you already have stats for, kind of like you can just buy art on the Roll20 marketplace, which feels like what Kyle was getting at with his comments.
Sorry if this was overkill, just felt it might be helpful to compare to an existing platform to understand what already exists as a way to see what they might do.