What if TLS won't be relevant in a few years to a decade? Bad actors can hoard encrypted traffic and have the data decrypted when the time comes?

Nothing. If you want perfect secrecy, you gotta use one-time pads with a one-time MAC, which is not really practical. Think having to buy disposable SD cards with 1 TB of randomness on them from your ISP, making your data cap very literal.

Even then, you'd be relying on the randomness source being good, which is not trivial. What if the ISP colludes, how would you ever know?

The most secure way to communicate is to not communicate at all, as always. Or to be more specific, to at least not involve an intermediary if you can choose so. Short of that, all that remains is the unproven hardness assumptions.