Has anyone tried upgrading by just changing the RD? (and chain/cassette)

According to this it can be done if you have an early version of the software, but if you upgrade the you need to replace the FD as we'll.

http://carltonbale.com/...ng-you-need-to-know/

However, it also says that you need to get all components with the same software build or it might not work. As the 11spd RD is obviously going to have a much more recent software this seems like an issue.

I'm tempted to just connect a new 11spd and see if it works, any downsides to this?