Always open the finder in new tab
Currently this is possible on macOS Sierra with the new "prefer tabs" feature.

To enable it, go to System Preferences > Dock > Prefer tabs when opening documents and select Always.

What are the downsides to this? Opening a folder will force open it in a new tab. That means that if you have a Finder window open in another space, the folder will be opened in the background with hardly any visual feedback. This may prevent you from knowing if a folder actually has opened and forces you to manually go to the Finder window to see the contents of what you opened. Additionally, this option enables the feature is all apps, not just in the Finder.