It has been proposed before... and clamped down.
It is their livelihood after all. They need people to spend and buy gold to earn their income.
Totally understandable. However, at the moment it means anybody with the bigger wallet wins, not the bigger brain. There's other ways to make money - unlock special units, special officers, etc. Imagine being able to build a tank with a level 1 army base! Or a bomber on air base 2. Right now, I leave a game and 3 hours later somebody had a level 3 army base up to 5 and 5 theatre defense systems he hadn't even researched all spaced out within 20 minutes. Because of that, working for 7 days straight to take him out by planning, upgrading, etc without it meant all that work was for nothing. I've seen this happen to many games, greed ends up killing them.
Most games don't have people like that... yeah, there are a number of people on Forums that are a bit disgruntled with this style and take, but nothing we can do about it.