The 4.0 API won't be available on NPM for a few reasons.
The Dojo dependencies which include dojox/dijit/dgrid/xstyle/put-selector and the build tools in util are not available via NPM, so dependency management via NPM wouldn't work very well.
NPM also doesn't lend itself well to downloading files to specific directories as shown in the samples.
When building with AMD, you'd ideally want each package in your src directory. You can setup dojoConfig to work around this, but again, you'd be pointing to bower_components for some deps and node_modules for others. This gets ugly quickly.
Bower is not being deprecated, they are just looking for more maintainers. That was more unfounded internet rumors that spread around.
Truth be told, by using Bower, we can make sure that users get the correct dependencies to do local builds. In our case, it really is the best choice at the moment.
You can see a demo using 3.x to do local builds here.
That's not to say that there won't be an NPM release in the future, just not with 4.0.