A 4K 2 hour movie is about 40GB. Most modern smart TVs around 32GB of RAM and can probably devote about 20GB of that to buffering a stream, so yeah, that should actually be doable.
Most users are not streaming 4K, it's a very small fraction of streams. Even those that do tend to have only about 4-8GB of flash, which is about half used by the operating system alone. RAM-wise, you're definitely off by at least an order of magnitude there.
M