iPhone 5S on Virgin Mobile USA

It's $100 cheaper than any other unsubsidized iPhone 5S. But my biggest concerns are resale value down the road and unlockability.

The Virgin Mobile iPhone 5S should be identical to the Sprint model, and the Sprint model should have the hardware to support both CDMA and GSM as well as LTE on every carrier, right? So does that mean if I wanted to unlock the Virgin Mobile 5S and use it on, say, T-Mobile down the road, it would work? Can I even get it unlocked?

Also, if it truly is stuck to VM even if it is unlocked, would the resale value on the 5S be far lower than a 5S from any other carrier, enough to negate the initial $100 savings? Considering how often I switch phones I'd almost certainly want to upgrade to the 6 next year so resale value is pretty important.

I'm really annoyed that Apple made the 5S and iOS 7 so compelling. Sticking with my Nexus 4 and upgrading that every year would have been so much cheaper...