Nothing. Well bandwidth and hard drive space but nothing else.

How do you define "economic node'? What sets them apart from any other node?

Nope. You enforce and don't enforce the rules you want for yourself. Everyone do the same, everyone choose their own rules.

So what happens when every node enforces a particular rule?

The beauty of bitcoin is that there's no need to "enforce" rules to others. There's no need to "vote" to decide which rules to enforce to all. Every node choses its own rules and decide to be in consensus with the group of nodes that has similar rules. So simple and so powerful. No voting.