"its "closed" architecture seemed reasonable. How else would one implement persistent two-way links"

That's a great example of a concrete implementation detail - unbreakable links means a central link database - that has significant implications in the shape of the vision. For example the only way I can think of to do unbreakable links but also distributed is an immutable public ledger perhaps something like a blockchain. And now we can talk about specifics like what other properties does a blockchain implementation shape? What does a database app with HTML forms and such look like? But did Nelson understand this? Can anyone cite an implementation source that goes into Nelson's analysis of this stuff?