Don't know where to find the article I read again, but Airbus has said an A380 built in a PAX configuration can NEVER be converted to a Freighter, the A380F was/is totally separate. So if considering re-sale as a freighter down the line forget it. It's not well known, I saw an interview where SIA think they'll convert their A380s to freighters in the future, it's not going to happen.
If I remember correctly the upper deck floor height is different and there are problems fitting the cargo doors to a pax A/C.
One of CXs problems with the A380 has always been the lack of VOLUME in the cargo hold once it's full of all the pax bags and the crew rest module.
Next time your flying any of the CX A/C on a long haul trip which has a full load of punters, ask the load control guy how many LD3s you have full of bags vs the space available for cargo.
If Airbus build a -900 then I think you'll see CX make a purchase.
Meanwhile I hope the -8I gets ordered as a stop gap but I doubt it.