I doubt any FOSS restriction is doable at all. As for the supply chain - xz showed this is indeed possible… But no one can guarantee that every encrypted client would be able to get such a well-hidden backdoor, and that it will stay undiscovered, and that it wouldn’t be invalidated with an update… But yeah, the only way this can be combatted is having more eyes on such software.
Counterpoint - younger generations grow up in the same poverty as their parents (so that any subscriptions are unlikely) and even if they don’t - their media needs may not fully align with what their parents would buy. So children in my experience do find ways to pirate. Maybe not the best ways, but still.