When you login with your character on friends computer it *should* be checking what version you have access to and then download it since your account is flagged for it. This is of course assuming they are not going with two separate launchers.
Printable View
I know this isn't FFXI, but this is also ARR's first true expansion, so there's no precedent; FFXI's PlayOnline launcher only downloaded the content necessary in the event expansion gear walked back into standard areas, but did not download the full content even if you had it registered. You still had to run the install disc. Granted, this was in a considerably less digital age, so that may mean nothing, and the content "lock" will (hopefully) come down to only which platform/expansion licenses you have.
My guess is if you have the expansion on one platform and not the other it may just flat out deny you the ability to log in. There would be too many checks in place to determine if you're using non-expansion content or not.
* Is the player the new race?
* Is the player currently equipped with the new jobs?
* Is the player located in a new expansion-only area?
* What if the player tries to access expansion-only content while using non-expansion content, even if they have it unlocked?
For simplicity it will either deny all characters or simply any characters that have been marked as "expansion accessible". By that I mean if you have any expansion-related content unlocked it will simply lock that character out from being used on a platform that doesn't have the content purchased. However I still think it'll just flat out deny any accounts without the required keys for that platform regardless if they have it for a different one. As for CE items I figure you only need to buy the CE once, standard will suffice on any other platforms considering you can only obtain them one time. Of course that also means you could probably buy the Collector's Edition on say PS4 but the standard edition through say Steam and still get the collector items.