We haven't rolled that out to the hostdb yet. Most of the host works in terms of public keys, and parts of the renter works in terms of public keys, but the hostdb still operates mostly on addresses.
@johnhowell has started work on the hostdb, and one of the goals is to (finally) fully support public-key based hosts. Even then, the network won't know about an updated/changed IP address until a host announcement hits the blockchain, so it will definitely hurt a host's visible uptime.
I'm not sure when the hostdb changes will be ready, but they are high priority because we're currently layering the final defenses against the easiest types of attacks against the Sia network.
I know that we are working on a lot of things in parallel right now. I'll go into detail on all of them more in our next roadmap update, which I plan on announcing next Tuesday.