Sharing the file is no problem.. under normal circumstances..  I agree.

But all the current methods, for the 99.99% of cases where neither party has access to an external IP or a NAT routeable address.. etc,  use a centralised intermediary.

Is there a way of delivering the data over a simple p2p network - in a decentralised way - much like LN  (where you are guaranteed payment for your work - hence more likely to offer your services) ?

Thought experiment as much as anything currently usable..