I think it belongs for the foreseeable future.
This screen - https://cloudup.com/cUp4Q3nHv17 - is only a precursor of things to come if you click Install. There is no friendly way to undo that process and the result itself can be pretty unfriendly. You could go back by removing the remaining defines and live in single site mode with some extra tables, but it's an ugly process.
The admin interface and workflows for a single site are much more developed than they are for multisite. A completely different experience awaits. I think for now it's nice that someone needs to lookup how to create a network before doing so.
I think I'd like to work backward and see constants like MULTISITE
and SUBDOMAIN_INSTALL
become less important first before opening the doors completely.