Andy,
Nice bike, got Di2 on my current bike (mix of Dura Ace and Ultegra) and would never swap it for mechanical. I'm hoping to upgrade the battery and WiFly bits to the new R9100 so I get synchro shift, not because changing front and rear really bothers me, just love the idea of seamlessly shifting up and down and letting it sort out the front and rear!
Went with a mate to the Specialized superstore near Bristol last week, really nice guy in the store took an hour and a half to show us almost everything in the store, including the new Dura Ace, SRAM etap and several very nice bikes.
I'm interested in the new Specialized Roubaix, but want it with R9100 di2, which hasn't really been released yet and may be a while before it comes fitted to the Roubaix. Thought about the etap, very clever wireless shifting, but I'm so used to Shimano (and it's very pricey). Could be tempted with an Ultegra Di2 and then upgrade various bits over time, just like my current Trek.
Came away with a crazy plan to get a custom build around an S-Works Roubaix frame, with the new Dura Ace di2 due to release any day now, and some light weight carbon disc wheels. Totted it up and decided domestic harmony would be wrecked, so perhaps the "start with the Ultegra and replace a bit at a time" approach may be the way to go...
Geoff