I think that burning cities could be advantagous in some situation but I would imagine that most of the time it will just be a feature thats available that is never used. Personally I would rather just "Abandon City" with no CP loss for doing so. Burning cities for Speed 3 would mean 15 CP lost, which is about half of CP thats needed for most cities after a certain point. Infact early in the game it would be equal to not conquoring a few cities.
So yes, Im okay with this getting implimented, I just doubt that I would ever use the feature myself.