Fair enough, although I dont think it would meet weaver 80/20 rule đŸ™‚
If you think about it, you have to go to each page at least once to set it up, how hard is it to give it the body class then. If you think of the design later, you still have to go back to the editing page to get the page ID #, you can then set the class.
So I understand it would make it easier, but I am afraid it probably represent too small of a user scenario to warrant weaver’s effort.
Nevertheless, feel free to post your suggestion in the suggestion forum