Breaking an Omnibus apart requires actual manipulation of the book file. This clearly violates DRM restrictions. (Just anoter reason to avoid DRM).
Would I rip apart my paper edition. H--- No
So why would I do this with an e-edition (other than I could if no locked)?
I think the solution to the omnibus, is x-reference records, Where title, author and original series index are entered, but it places a "dummy book" that, when opened (attempt), redirects to the Omnibus edition. (A 3 title omnibus, would have 3 x-ref records. It would really be cool if the link could force a jump to the actual chapter-section in the omnibus (may not be doable with all formats or reading devices).
This would work really well for anthologies, where Author information currently gets muddled (one long list). Now we can create an X-ref for each Author-sory pair.