Domains will almost certainly remain as services but be given a designation as domains so they can be displayed a little differently. That seems to be the simplest way forward. There will still be a plugin, which will handle creating a pricing grid, syncing renew dates, whois etc. The idea with the pricing grid is that packages will have the ability to defer pricing to a plugin. So, the idea is you could create a single package and not set any pricing, and it will obtain pricing from the plugin/pricing matrix for all TLDs and register/renew/xfer.
This is subject to change to some extent, but should give you some idea of where we are headed.