@jswinden: Yes it's me.
I'm keeping a roadmap of upcoming features on Marvin's website (e.g. Calibre Server and more). I'll make sure to add a 2-column layout to the list.
There is a new update planned for launch next week but the Apple review team go on shutdown for Christmas so I think it's unlikely I'll have 2-column layout ready before then.
@Synamon: if you enjoy Dropbox support, you'll be glad to know that today's update added a new search feature and the next one has even more Dropbox improvements.
In the meantime, I hope you enjoy using Marvin and please get in touch if there any features you'd like to see added.