> Oddly, it would also imply you could potentially generate entirely new files out of the network; in an infinitely large network, you wouldnt even have to specifically upload a new file — the hashtree would be enough, and the network would find the pieces to compose it

It's vanishingly unlikely that this would yield useful results in practice.

In a moderately-sized network, however, if only a few contiguous bytes in a GB file change, then only a single block would need to be uploaded. (if the original file is sufficiently available already)