As the network stands now, all nodes are treated equally. Why should this always be the case?
There is nothing currently stopping anyone from running multiple nodes, which is fine, provided no significantly large number of nodes falls under any particular entities control (colluding nodes are viewed as an entity).
My point is that if I (or any entity) wishes to support the network with multiple nodes (even over tor) I should be allowed to. What is required is a disincentive to be dishonest. Requiring proof of passport doesn't remove the incentive for dishonesty. It merely creates an artificial and arbitrary limit on node creation.
Proof of stake requires economic commitment to the Bitcoin ecosystem, much like proof of work does. This makes it prohibitively expensive to build nodes to create a Sybil attack, exactly like proof of burn would, but without the cost. It's impossible to fake and can (if required) have a strictly enforceable 1-1 relationship with a node.
It also provides a powerful disincentive to generate dishonest nodes. Coins in addresses used in a proof of stake by cheating nodes may be voluntarily neglected by miners. The opposite is also true, and co-operative nodes with honest and reliable reputations may receive donations or prioritised transactions.
Agreed, having private keys on a remote node with a large balance isn't a good idea. But there are solutions to this. For example: A large balance offline wallet could be used to publicly authorise an empty address as a proxy for the offline wallet.
We all know Bitcoin is supposed to be decentralised, but just as importantly: It's supposed to be a free market solution. It's the reason Satoshi ultimately wanted artificial and arbitrary limits removed from the system.