Earlier quoted context omitted.
> Since this engine is GPL-licensed it seems like any game built with this engine would then also need to be GPL-licensed, correct? Yes, mostly correct. In order to comply with the GPL, and distribute game binaries, you need to make the source to any game you make with it available under the same terms. Technically that does not mean that you have to distribute the game under the GPL, but in practice that's how you w…
Could just release the game engine binary with a separate loader for assets and license check... Utilizing steam for distribution and in game features could help too.
It's also not assets that are the problem, it's the game-specific code.