You're assuming that smart lightbulbs are to be trusted. You can't trust them, neither can you trust most of the software you run in your home network.
Take a simple app crash report on your desktop computer. Assuming i'm using VPN (but even without it, it's an issue)... With NAT, your crash report will contain network adapter address: 192.168.0.x. With ipv6, you're disclosing your /56 (or /64) ip range... disclosing your physical location, your ISP, ...