Tarantool EE uses etcd as a centralized-config backend (config.storage / etcd source in TT 3.x): on boot it reads config from etcd then opens a Watch with prev_kv set to diff old-vs-new config on live reload. So Watch prev_kv is a first-class ecosystem consumer, not just a conformance checkbox — it gates drop-in TT EE compatibility. Feature is implemented (app/etcd/watch.lua lookup_prev_kv); the open work is the TestWatchWithPrevKV conformance case (tarantool-etcd-9z2, Phase 5f).