Its a worry, but its too early to be sure what the long term effects will be. We will have many eyes on a lot more code. There might be a rush of reports that slows as all the old vulnerabilities are found.

Closed software still has many people with access to the code. Governments or researchers have been given access to lots of critical source code. It can also be leaked. I wonder whether attackers are going to be more willing to bribe people with access to source now they have better odds of finding vulnerabilities with limited effort.