I don’t think they’re going to drop support for local backups any time soon. There are lots of enterprise customers relying on Time Machine who will never switch to iCloud. TM can also be configured via MDM settings and is a really common solution for Mac IT administrators, so it would take ages to deprecate it.
"There are a lot of enterprise customers using Xcode server". And poof, it's gone and there's now only the Xcode cloud service. It would not take ages. It would take a single release which no longer supports it. Complaints? Keep using the old one or subscribe.