I do development on my elementary OS machine.

Does elementary still return their release codename instead of the base ubuntu release for `lsb_release -cs` in shell?

Yes, because elementary OS is not Ubuntu. In the past, we carried newer versions of GTK or other core libraries, so pretending to be Ubuntu would actually do more harm than good.

However, we have added an `--upstream` or `-u` flag to lsb_release like other Linux-based OSes to point to an upstream release if the downstream release is not supported. I believe this has been adopted for installers of tools like Ruby and Node.

Makes sense, I hope all installer tools will start using it

That's correct. They do show the Ubuntu build on the "About" section.

What else do you need for an OS now? As a developer what I need is a browser a terminal and an IDE. Everything else just need to be fast and non-distracting.