To be clear, there is no guarantee that a draft mode will ever be added. While it’s something we’re discussing, no decision has been made.
I can see the utility of a draft mode for the mobile apps, but after doing some thinking I can’t say I see the need for one if you’re using the web uploader. You can already take all the time you need before making observations via the web.
And if a draft mode is made, there would have to be something like a 3 day limit where observations get automatically published to avoid large backlogs.