I think not. Sprint will have enough spectrum to play with that it wont be a "need." IF a company like nTelos bars Sprint from entry into that market then i could see Sprint making a play at them.
2.5/6 Ghz will not boost coverage. If you looked at the total coverage area on a heat map for 800,1900,2600 Mhz you would see 800 will provide "stronger" signal within the coverage zone and increase the coverage "bubble" that already exists from 1900. If you look at Sensorly compare Verizon's coverage to Sprints; VZW has a much darker purple. Sprint's 800 will do the same for their maps since at that point we will have signal from Sprint everywhere within the coverage zone, and Sprint has site spacing equally as tight as Verizon where i live. 2.6 is not a coverage booster, it has less reach and significantly lower propagation "power" than 1900mhz even. It is simply for capacity.