The reason I think a "speed at distance" system would be easier than a "dynamic performance predicting" system, is the basic equation a=f/m.
In this equation, acceleration is changed by either an unexpectedly low thrust level (including unexpected drag) or an unexpected weight. Depending on the level of sophistication desired in a dynamic predicting system that might cue pilots for actions during takeoff (such as increasing thrust, etc), the system has to accurately figure out whether there is a mass problem, or a thrust problem. This would be complex and the system could never be wrong for safety's sake. Then the system would have to dynamically change and display its prediction based on performance changes made by the pilot.
The "speed at distance" system would be much simpler to design, certify and implement, as there would be no prediction (after the initial speed at distance plots were generated), and no action cues would be generated by the system for the pilot (thus no possibility of false warnings or false action cues). The pilot (PNF)would simply read the displayed numbers and use his judgement instead (and follow SOPs etc).
A HUD display generated by this system would be possible as well.
