The problem is that it hurts new players because they're more likely to be attacked with structure killers and so lose the ability to produce ships to defend themselves, which means they get roided more and can't defend themselves and so on. Basically it works out to a bit of a vicious circle.
But nice try though
EDIT: A personal thought is to give -1 production eta for every 2 factories you have above the first factory, and cap this at a production eta of 3 ticks. Of course, there are different types of factories, but I wouldn't vary production ETAs for different classes of ship - instead, whichever factory you have the most of is counted, so it wouldn't matter if you had 1/1/8 factories or 5/5/8 factories.
The base production eta is 12 without any race or engineering bonuses.
Code:
Factories | ETA
----------------------
0 | 12
1 | 12
2 | 12
3 | 11
4 | 11
5 | 10
6 | 10
7 | 9
8 | 9
9 | 8
10 | 8
If anyone likes this I'll make a thread for it so that this one isn't derailed anymore.