Dick,
I agree with the fact that trims are speed dependand, and this is the key problem IMHO. If it would be possible to reduce right thrust with some almost-symmetrical fuse lateral surface, then no rudder trim and such moments on the yaw axis, which could let the plane fly the same at slow speed - max throttle or max speed - idle throttle... at least this is my understanding, if I'm wrong please tell me!

From what I understand, there is also a tradeoff on the yaw axis, between stability and good KE behaviour: the former requires a more aft surface, the latter a more forward one. Am I understanding you correctly Dick?