I think you should speak to Mark first.
When I used to have a website, I got more than a one offer to attach my site to other's. Aside from remaining in full control of it, the thought of having to blend my design to somebody else's was definitely enough for me to refuse. It may not have been the most professional or amazing one, but it reflected the time and effort I put into it. It was mine. Switching the design to another site's would have been like writing a book and then have somebody else keeping the story but rewriting it.
Of course, it may not matter to Mark. I have no idea of what he would think.
Your theme looks great. I don't have suggestion since it never even occured to me to change it. I guess I'm fine with the way it is now.