We just edited the Olympics in immersive. (We've edited them 5.1 discreet since Beijing 2008, pro-logic surround since Sydney 2000)
Basic approach was channel (rather than object) based. Truck generated bespoke 5.1 and on-passed the 4 host height channels + extra 4 spot mics. The immersive part was then mixed in control room as it aired (trucks generally not that well suited for immersive monitoring).
Edit was mostly to replicate/match truck 16 channel output but plenty of rebalancing, replacing, revoicing. Had to keep immersive tracks matching the rear surrounds.
Used Avid, would've possibly been a bit easier with PP adaptive tracks.
FCPx doesn't have output or export options for it to work, at least not as far as I could figure. Network + freelance editors heavily tied up with Avid anyway.