Swapping out cassettes sizes on a Di2 bike
OK, so I'm vaguely considering getting a new road bike, one which has di2 and disk brakes. My current road bike has rim brakes and mechanical shifting. However, one thing I like about my existing road bike is the gear ratio. My lowest gear combination is a 36 in the front and a 34 on the cassette. All of the di2 bikes I've seen, however, either have a 34/28 or a 36/30 as their lowest gear combination. I was wondering how involved it would be for my LBS to swap out cassettes on a di2 bike in favor of one with a larger gear. When I had it done on my existing bike I needed to get a new rear derailler. I wouldn't want to have to replace the di2 component just to have a different sized cassette. Any thoughts?
Second question: is it worth getting a new road bike to get electronic shifting and disk brakes? Or are those things overrated?