I would like to wait and see what the official answer is, but I 'THINK' I have a code hack that will do what you are wanting if all else fails.
What you are wanting is very similar in nature to changing the color of the text based on profile type that I have done on my site.

Hello Vital,

Regarding

Is there a way to restrict who is able to post on the homepage wall?

I am not sure if I understand you well. Are you referring homepage wall to dashboard? If so, I believe there is no setting to configure this but you can tweak the code. Can you explain more on this issue so that we can understand you well and able assist you on this issue.

Please be advise.
Thanks.