Personally, I'm just going to start ignoring Moshe after this, because he seems to only repeat himself as I apparently do not break down my posts into quarter-step by quarter-step.
It would take a large overhaul of the system itself to balance it, something that would end up making many others angry.
If you could buy promotions, then the Promotion system would then become useless. This is why you cannot buy promotions right now unless you count paying for the barracks/civics as "buying promotions".
THAT is why it is impossible to balance without messing up the game. I've noticed that you, Moshe, have used "Well, change [Already fine thing in game] and the idea would work fine]", which is fine, until it starts getting TOO large just to make way for a single idea.
Give tanks the special ability against gunpowder units, and it's UNDERPOWERED. You see, the balancing issue is what brings this idea down to it's "knees".
You want me to be specific about the "Unable to be balanced" thing? So be it.
Your idea cannot be balanced without editing many other things in the game, and even then there will be many issues. It seems like your ideas are mainly to make the game streamlined and easy on all levels.
Also, I do realize that no one would send 10 tanks... Unless there are 10 infantry standing in a city, and even then, it would probably be followed by a much larger stack. It's an example.
Oh, and rys, I HAVE thought about making it sufficiently expensive, and, to be honest, I don't think it can be. It would have to be a different number for each unit, however, it would end up unwanted if it really WAS sufficient.
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