When I tried to commit a proposal, a message (as shown in the image) appears/
Yes I can commit to only three proposals at a time.
If I want to commit to any other, I have to uncommit or any of the committed site must be launched in beta.
Here, in the three sites,
Computer Science Educators are in Private beta
DevOps are in public beta.
So, at present I committed to only one proposal, Interpersonal Skills.