The Di2 maintains compatibility better that SRAM Red. It is more durable. I was a long time MAVIC Mectronic (1990s wireless) user and welcomed the cables even though wireless is convenient.
We had a SRAM Red bike. Then got another SRAM Red bike with year newer components. The brake lever parts were not interchangeable. They have broken, and I needed to swap parts.
I have a 2010 - 10 speed Di2 (Gen 1), and three 11 speed Di2 (Gen2) bikes. I have the sprinter buttons, TT shifters, hill climbing shifter and have put junction A from the bar stem to the seat post. I've wired a few bikes for friends. I'll be getting a few 9100 (Gen3) parts soon. The Gen2/Gen3 are all interchangeable. The ETubes let's me reprogram stuff.