This idea is bad. VERY VERY VERY VERY BAD!!!!!
It makes it so countries without a lot of startup money have to inflate their economies like balloons in order to build just the tax collectors; not to mention armies. I just played where, after an initial war against the Teutonic Order (mainly to unload my massive army in a useful way, as opposed to disbanding it), I could barely maintain a 10k army. I only had 100 starting cash, which I used to build 2 tax collectors. But then I had to start inflating. Since I built the tax collectors on Jan 1st, I didnt get the benefits until the beginning of the 3rd year. Which means that until that point, if I wanted any cash I had to draw it out of my economy and get inflation.
However, in a few years I had recovered. Lithuania, however, had not. I ripped through them like a knife through butter. They could barely keep a 10k army together and I was hitting them with 40k. I was able to take half of Lithuania with no problem. Then came the problems. I didnt have hardly any money (despite expansion) but I did have a lot of enemies. Then the BB wars started. Oh, it was quite brutal. My vassals were cancelling and DOWing me. Nasty stuff.
The gifts the AI tosses around end up being extremely hard on the player. A 20k army for a one-prov minor used to be a pain in the arse, but no big deal. Now, that army is bigger than yours. It is hard to keep a decent army in the field without massive inflation, much less lose soldiers fighting revolts.
With this situation, I see very little chance for the AI working out right. Everyone will be running inflated economies just to keep up with their neighbors. It benefits major powers much more than ever before. The AI, who had problems with inflation before, is just pathetic.
While this may make the game more "historically accurate", it has made it much less fun. Having a crappy economy for 50 years is just annoying and boring.