That is a change I'm not particularly thrilled with. Plenty of times the AI placed cities seem to have fairly poor benefits (2 production and 3 food, for example), so rather then live with a sub-par city I just remove it and see if there are better alternatives.

Other than that, I'm eager to see how the new version plays

You could also just make the barren tiles slowly revert back to normal tiles after 100 seasons or something like that. A spell to restore it could also be added, though it is sort of weird to think of a rampaging army that lays waste to the land and immediatley plants seeds and tries to build it back up to what it was before.

I personally like the barren land idea and as Seanw3 mentioned, there's a restore land spell to balance it out. Since the number of cities has no impact on the rate of city growth (only maximum population), capturing cities often becomes a burden - you capture them and incure lots of maintenance costs and they dilute your pop growth so it takes longer for cities to level up. I have often just kept cities to deny the land to the  AI rather than because I actually wanted the city so I welcome these changes - I hope Derek takes it further and brings in the forest fires and scorch spells from Fall from Heaven. 

Restore land doesn't actually work. In fact I'm pretty sure they come in a set of 'make this land empire type' and 'make this land kingdom type' rather than have any effect on yeilds. Mind you this is pretty rediculous for a master spell and perhaps the function is supposed to allow players to settle these regions later game, but perhaps it's intention is to make current lands more fertile. The actual function of this spell is unclear.

Even if it was though.. there is little chance the player you are attacking will have this spell to use when they (or you) come to town, preventing any sort of comeback if you get a city destroyed. Perhaps the land could become barren for a short period of time and gradually revert to it's normal output, to prevent pioneer spam.