My own personal thought on this is to do it like ACDSee have done for v4 where each screen can be put anywhere. The player could for instance be dragged and docked at the top, the left, right, bottom etc. playing now the same and so on.
That way people could customise it exactly how they want it.
For me, instead of Playing now and a visualisation window, I'd probably have the playing now there with the media search above it. etc. I'd then put a playlist window on the left, below the media library as I have it on a high resolution and so could easily display the contents of playlists here next to everything.
Taking this even one step further would be so that not only could they customise the view, but they could customise each view.
Like for me, when I'm browsing my media files and they're being shown on the right, at this time I want the properties window, but when I'm in playing now I dont want it there still.
I'd also definitely like to be able to customise the columns that show at different times into different orders.
When I'm using the explorer mode I'll want file name somewhere near the beginning, when in Media Library I'll not want to see it at all pretty much.
I'd like to be able to create different view schemes (for columns)) which I can change between easily, and also display which parts of MJ show where on different screens. For the playing now I might also for instance choose to have the DSP studio docked somewhere.