AFAIK there's no wxLayoutManager, instead we have wxSashLayoutWindow's. A solution for the layout problems(?) is to replace the wxMDIParentFrame with wxFrame, and turn the cbEditor (or EditorBase actually) into wxScrollingWindow instead of wxMDIChildFrame.
Then we can use wxSplitterWindows for the layout, and a wxNotebook for the editors, so everything in XRC.
I guess we haven't asked anyone to try to do that, but once beta8 is released (which i really hope it's this week *ahem*
), we'll switch to a single frame layout.
BTW, if anyone wants to experiment and try to do the conversion for us (we'd be REALLY grateful!), he's welcome to do so.