Very unlikely that you'll see mass-use of LLMs as opponents. Enemy AI in most games doesn't need the level of complexity that machine learning demands. (Ignoring computational costs for a second.)
The main goal of an enemy AI isn't to be the hardest thing in the world, it's to provide an interesting challenge for the player to overcome. It's not necessarily difficult to make a hypercompetent AI in most games, but that also wouldn't make it very interesting to play against. Most games have finite states of logic, just large enough to the point where a human would have trouble finding every solution to it (although humans tend to be very good at pushing on the edges of these states to find ways around them).
Even in games where the amount of state is much higher than usual, you rarely want a super AI; nobody likes playing against an aimbot in an FPS for example.
Factorio is an outlier because unlike regular games, the true condition for a "victory" is almost entirely up to the player. You can make a rocket in non-DLC Factorio (the games victory condition) without building any factory at all beyond the most basic structures for stuff you can't handcraft. It'd be extremely slow, but it's an option. That's why the benchmark for this sort of thing is more efficiency than it is "can this work".
Civilization (VII just released) is famous for having the harder difficulties be harder because the AI cheats. If the game was harder because the AI was smarter instead of it cheating, it would be worth it to players to upgrade!
As an opponent that would be indeed unfun, but as a sparring partner / coach in a competitive game (fighting game? Rts? Moba? Puzzle game?) that would be useful.
The main goal of an enemy AI isn't to be the hardest thing in the world, it's to provide an interesting challenge for the player to overcome. It's not necessarily difficult to make a hypercompetent AI in most games, but that also wouldn't make it very interesting to play against. Most games have finite states of logic, just large enough to the point where a human would have trouble finding every solution to it (although humans tend to be very good at pushing on the edges of these states to find ways around them).
Even in games where the amount of state is much higher than usual, you rarely want a super AI; nobody likes playing against an aimbot in an FPS for example.
Factorio is an outlier because unlike regular games, the true condition for a "victory" is almost entirely up to the player. You can make a rocket in non-DLC Factorio (the games victory condition) without building any factory at all beyond the most basic structures for stuff you can't handcraft. It'd be extremely slow, but it's an option. That's why the benchmark for this sort of thing is more efficiency than it is "can this work".