Why would you need TAS? The aircraft flys the procedure, and is bound by the leg speed or other restrictions...I can put a 3.5nm radius or a 10nm radius....it does not fly one faster because it is a smaller radius.
Look at the RNP procedures in Canada with WJ, you will see short finals with the 737NG with 1.5nm radius RF legs, that is the bank limit of 25 degrees. (with 50 kt tailwinds)
I have already done this with RNP procedures several Airbus variants ...The 777 with the Smiths does not...
The question was which FMS type can do an offset less than 1nm.