>However such a huge investment may force them to "overscale" in order to be able to reach the expected return (by the VC).
But how can we know that's even an issue? There are a hundred hypotheticals here (both positive and negative), and focusing on the ones that would only be the case were Andreessen Horowitz & GitHub unwise companies seems unnecessarily negative.
Now, if there were reason to think any of them, that'd be one thing. But we only know there was a huge investment in an awesome company from a great VC firm.
I'll leave it to the company to describe what they are going to do (and they talk about some of that in their blog post today). I can say that my partner Peter and I have spent a lot of time with the guys over the last several months, and there is no daylight between their vision of what they want to do, and what we would want them to do.