This can already be done. Please familiarize yourself with the Help Vault before making a new feature request.
- Settings → Files & Links → Default location for new notes. Set this to “In the folder specified below” and you can choose any folder or subfolder that you wish.
- Daily Notes and Zettlekasten plugins can also be configured with their own custom folder location.
- With the Obsidian URL scheme you can create new notes in any folder and file you wish by triggering a URL. You can create new notes, or append to existing notes.