It would be very possible to expose an API that has a random number generator with a configurable seed value, though.
You know what would be even better? If you could manually seed Math.random() to begin with. But yeah, I can see these being very useful for predictable random number generation!
There is very little stopping an engine from providing a builtin random number generator that can accept an arbitrary seed.
I would consider at least having the ability to seed a generator, even if the results were inconsistent between engines, to be a good thing.