Leonard probably asked for powers (like meta humans). In the new 52 comics The Rogues placed their themed weapons into Elias' http://dc.wikia.com/wiki/Darwin_Elias_(Prime_Earth) genome recoding device, and fused their DNA with the weapons. Captain cold then gets the power of Cryokinesis. Leonard probably wanted Barry to make him into a meta-human, so he could be more powerful.
Sorry, im not 100% sure.