While the idea may seem nice, I fear that this would be a huge imbalance for the players if it gets implemented. That's because players tend to keep their units alive way better than the AI does. As a result, you'd get super powerful stack of troops (high leveled) if you let them upgrade everything. Worse yet, the player would only build a couple of troops and pretty much never need to build more.
As it is right now, you want some squads to help exploration in early game, then another set of troops when you're ready to take on the really big stuff. This at least makes the player decide on what they build in their cities. If you can go without troops until much later, power to you.