Hydraulic disc Di2 sounds like the perfect setup for a touring bike. I've run it since its inception on both road and gravel bikes. In my experience, it's more reliable and requires less maintenance than cable actuated systems. You can ride it weeks, even a couple months, between charges. My only caution: When parked, don't lean the bike in such a way that a shift button is pressed. That's the easiest way to drain a battery prematurely. If you take that precaution, Di2/hydraulic should give you worry free service for a long time.