Currently you can't see the total cost for a technology but you can see the total number of turns to get the tech. By changing your research output you can actually work out the research cost; i.e. if my output is 20 rpt and the time it takes to research a technology is 4 turns and I keep upping my output till it hurts 30 and the turns to complete drops to 3 I now know the cost is 90.
Seeing as this is deducible, why not show research cost? This would allow people to calculate how long it will take to achieve a certain strategy 
If the cost depends on total amount of technologies you currently have then just showing the current value of a future (read not currently research-able) tech, even if it changes as they research other techs on their way towards it, it gives a rough idea and at the very least helps for current techs