It is a challenge. The larger gear for the servo arm is needed for mechanical advantage. The casing will have to be redesigned to house that gear. But if it was made to fit closely, it could protrude a little above and below the trailing edge. It still would be a lot neater than a control horn with a push rod or pull, pull system plus control horns.
As for the integrity of the trailing edges of the wing or stab, the solution will follow. I believe any structural problem can be solved. The same may be said about installation, inspection and servicing of the servos. The rudder servo should be relatively easy as the end of the fuse is thick.
Balance is important for our aircrafts. I know of a member of our club with the elevator servo mounted directly underneath with a very sort push rod off he 2 lb fanjet. But his plane has a very long nose section and the Li Po battery is up front in the nose.
Our planes for this "new generation" servos may need an innovative approach to balance.
All this dreaming of a new type of servo can only become a reality if the designers and manufacturers would embrace the idea. Then when the competitions begin, and only then, we may have servos that will make our hobby easier and better. Meanwhile, we can keep dreaming.
I cannot imagine a full sized airliner having push rods and control horns on the control surfaces. Can you? How about any other problems?