It's been said that all of the warlords features are to be included in BTS... So could it be possible to see a General teaming up with a spy? I guess a better question would be: do spys get experience, like military units? I don't see how they could do it, with the great spy aswell...but I think its a pretty cool idea.

From what I know you build up Spy point through experience. Anyone know if your spies can be unmasked and executed like in 3?

No, you don't. It was expressly said that espionnage points work like gold, science or culture. There are even spy specialists in cities. So it does not work anything like Great Generals.