The issue right now is that mech exists in higher level groupsets because they need them to meet a pricepoint.
If, for example, you had a jump from Tiagra Mech to Shimano 105 Di2, you basically have a $500 vs $1500 groupset. That's a big gap price wise. Solution will be of course to increase the price of Tiagra mech when they bump it to 11 speed. Problem solved for Shimano. But then consumers will have $1k Tiagra groupsets when they were $500. Sora will go to 10s, etc..