The "create a copy" function is probably as good as it gets.
I think it would be awesome if reddit were to blur the lines between subreddits and multireddits. Many defaults have huge lists of dedicated subreddits for stuff banned from the default in the sidebar. If the defaults were multireddits newcomers could incorporate or exclude these specific subreddits into their version of the default multi.
Of course, I'm almost certainly underestimating how impossible it would be to integrate the two like that. Still fun to consider though.
