I know this was started in another thread, but my blindness could not find the right one so I started over...

I was reading through Carlton Dale's "Everything you need to know" on DI2, and came across some information I thought might be useful.

Apparently, the later versions of Shimano's update software (version 2.6.0 and later) updates the battery in a way that makes all the 10spd and 11spd bits incompatible (it was my understanding from the article updates that it is the battery update that is the problem).

The site does offer a "solution" of sorts, including a link to an older version of Shimano's software, which according to him allows the mix of derailleurs.

Two points were-
1. Once you update using 2.6.0 or later you can not go back.
2. Do not open the earlier software while connected to the internet so it will not look for and install updates.

Out of curiosity, and not discussed in the article, is if you replace the battery mount with an earlier version, install all the 10spd components and update using the older software, might you then be able to reinstall the 11spd bits and have a functioning system? Of course updated derailleurs may also be an issue, this also wasn't discussed from this angle from what I read. Then, may the XTR DI2 RD plug and play if you don't update with the later software...

I'm thinking some may want to at least have the older version of the software, especially if they haven't been jerked around by the update yet...