Originally Posted by
Lorenzo
There's no room in the eccentric shell for wiring
AFAIK. How feasible is it to run the wiring using the guides for the existing RD cables? (apologies if the question shows a startling ignorance of how DI2 works and what is required to install it;-)
It's possible to use external cabling for Di2, as Shimano offers an external battery option. However, external Di2 cabling is not ideal because of exposure to dirt, moisture, and snags. Here's an Velonews article on external cabling:
Technical FAQ: Installing electronic shifting on a bike without internal cable routing | VeloNews.com