From the way Sprint's Senior Vice President of Networks Bob Azzi was talking to PC World, LTE could be coming to Sprint sooner than later, thanks to a power struggle with Clearwire over their shared Wimax infrastructure. [PC World]
I really wouldn't be too worried about it when/if Sprint does get LTE turned on. Odds are by then Evo and Epic owners will be eligible for an upgrade and even if that isn't the case I doubt Sprint is going to just shit-can Wi-Max instantly. Odds are they will run Wi-Max concurrently with LTE for a while, just like Analog cell phones ran concurrently with the digital ones for many years. Who knows, Clear may want to stick to Wi-Max and Sprint will still let legacy WiMax devices use that network for as long as it's operational.
I bet Sprint's issues with WiMax is getting vendors to build them compelling hardware. Apple either has refused or would refuse to make an iPhone with WiMax opting instead for HSPA+ or LTE. I'm sure even their favorite manufacturers HTC and Samsung don't like having to make Sprint only 4G handsets. If Sprint moves to LTE it'll be easier for them to get new hardware.