Hi BOAC,
Sorry - but you are beginning to confuse me now. Have you started the conversion course already?
Now, once you 'inject' a speed input into the THS setting you begin to open 'maybe' doors onto the behaviour of the mid-Atlantic 340 and possibly 447 and others. I note the evident resistance in the AB community to accept that anything could be wrong but I do not admire it.
No one would design a system like you seem to suggest with
It would be a breeze for some clever software writer to give the THS access to a IAS/angle/alt/c of g table and have it automatically adjust its datum concept. He/she might then go away thinking, 'Haven't I done well? One less stream of THS follow-up signals associated with speed change. Look - it KNOWS exactly where it should be for 1g at 230kts, 190kts, etc'
How would it know where the C of G was with a full plane load of passengers doing the Conga from the front to the back? (e.g. Last TriStar flight from Dublin)
It might be controlled by FBW - but it's still physically a conventional aircraft obeying the same aerodynamic laws as your Boeing.