>And nowadays big data centers are basically just SDNed, and you might as well not be using IP in the data center at all, because nobody's routing the packets. It's all just one big virtual bus network.

The opposite trend is true in large data centers. L3 fabrics where everything is routed have become extremely popular because BGP (or custom SDN setups) can be used to migrate IPs and you get to utilize multiple paths (rather than the single path offered by STP convergence).