Cost index is available through software or AOM tables but as its calculated on the OFP why do you need it in the non certified FMS? Just insert the OFP climb cruise and descent speeds correctly and you have cost index
"Blue bananas" sound like unripened technology to me. What's wrong with FPA and vertical profiles? Perfect for continuous descent planning and easily achieved with one push and the turn of a knob!
Better still why not use vnav? Along with lnav and auto tuning you only need to remember to press APP at an appropriate time and all the other work is done for you. ( including using free speed to control the vertical profile rather that "random speed" as an earlier poster described it)