I thought about reporting this as a bug, but I suppose it isn’t if the headings to outline work as documented during import. (Not tested by me, because without this feature request the import feature is not useful to me.)
When importing a MultiMarkup file, I’d like more than the headings. Ideally, I’d like all the features to be supported … but the lack of italics is a showstopper for me. If italics are done, bold follows, and then … 
FYI I am using the current (Novermber 2016) version of Scrivener on OS X El Capitan, 10.11.6. Or not using it, because I don’t like the OS X native text editor, but that’s me and nothing to do with Scrivener.
Bottom line (as ZeroDay posted in a MultiMarkup output thread) improved import would be nice to have.
I am impressed by Scrivener, but I don’t think it’s going to work for me because My Favourite Editor doesn’t edit RTF conveniently, and I think I’m more attached to emacs than I am to the neatness that is Scrivener. However if MultiMarkup import became a fully fledged feature, I could do my main editing outside of Scrivener and take advantage of all of Scrivener’s cool organisational features without replicating them in a disciplined fashion with folders, files, naming conventions and having to deal with conversion to multiple output formats which Scrivener does well from what I read.