it’s started making me wonder how easy it could be for a node provider to own multipe nodes under different identities/entities, with the intention of eventually having full control over a subnet (controlling > 2/3 of the nodes), i.e. a sybil attack.
Yes, this is a concern. The Node Provider Technical Working Group is working on various ideas on ways to audit or check node providers, to make it harder for someone to accomplish this.
Technically, this risk is why every subnet cannot have more than one node with a single node provider. Each subnet being spread across nodes around the entire world also works against this risk, as it would be signficantly harder for a node provider to set up legal entities in many countries and form DC contracts in many countries. We encourage the community’s engagement with this topic!
The biggest requirements to become a node provider are both the funds to buy the servers (which can easily run $10k per server) and have the technical ability to manage nodes. Many people have one but not the other. The biggest issue with requiring a large staking amount is that it would raise the cost to become a node provider even higher than it already is, since any funds that are staked could not be used to purchase servers. (But one could argue that spending $100k on servers that are highly specialized for the use of the Internet Computer—and signing data center contracts which typically run for a few years—provides a similar type of “sign of dedication to the IC” as staking. The only realistic way to gain that money back through rewards is if the IC continues to grow. I do not think we currently have any way to slash someone else’s staked ICP, though someone else can correct me if I’m wrong.)