I'm with JSWolf on this one, unless you have an awful lot of gui control (and there will never be enough) I don't think all that many omnibus are going to split very well. For instance there are always things like the introductions and post book special features/appendices etc - do you duplicate those, put them in the first/last. What about the various inner covers, contents pages etc - some of it you want to ditch, others you want to modify so it looks like the first page of the single edition.
And then as pointed out there are the technical issues - sometimes shared resources, sometimes each book is completely self contained.
Good luck Jimm if you take it on - I'm not volunteering
