I’m not convinced open source would really help. I get the feeling that Mathematica’s underlying philosophy just isn’t a good fit for practical programming.
Two recent problems I had with LaTeX:
* If you put a \dfrac inside a table, the table thinks that the fraction is smaller and the line of the borders of the table collide with the numbers.
* If you need a different header height in your first page, you need some black magic macrology to get a not so good solution.