They wont do it so dont get your hopes up. Not to be a killjoy but if they intended to allow unlocking on older devices they would have said so. All info from sprint on this says "devices purchased after" Feb 2015.
Sprint LG G2 >> Current Owner >> Stock, Debloated, Rooted, TWRP'ed
Sprint HTC One >> Current Owner >> Stock, Unrooted (Till Kit Kat Comes)
Sprint Moto Photon >> Current Owner >> Rooted, Docked, Converted to XMBC & Android Media Box
TMO HTC G2 >> Past Owner >> Imo, The best Phone ever made design wise.