Unit Upgrade Trees

It would be nice if we could have upgrade trees for our units and personalize their abilities.

Example (purely theoretical):

tank to light tank -2 atk -2 def +4 range +2 view Costs: 10,000 SP
Then from light tank to Panzer +1 atk -2 def +4 range +2 view. Costs: 20,000 SP to uprgade

Come up with ideas of your own.

Not sure whether this is such a good idea, in general.

How about these "unit personalization" upgrades only apply for certain strategies? Light tanks make no sense in IF (thematically, that is), but they fit Blitz well.