Lightroom mobile can only log into one Adobe ID at a time.
Only one catalog may share with an Adobe ID at a time.
Even if you have two Adobe IDs, each attached to a Creative Cloud subscription you could share from two distinct catalogs on two distinct computers but your mobile device could only see one at a time.
This seems shortsighted.
I am not sharing a catalog - that isn't even an option. Under a single Adobe ID you are allowed to have a desktop and a laptop run the lightroom software as long as they are not being used at the same time by different people. I want to share unrelated collections from two unrelated Lightroom catalogs to a single iPad.
What if I have two separate Lightroom catalogs on my desktop computer; are you saying that I cannot share collections from both catalogs at the same time from the same computer?
Again, this seems shortsighted.
This cannot be the only time this has come up.
Certainly not the first time, but just think too of all the complications that would have to be resolved. For a simple example, what if the same image is recorded in two catalogues with different settings? It would be tough with a single "catalogue" on the iPad - which settings are right, do you want each collection to be named something like catalogue A collection XYZ? Or would you create a UI so the users switches between catalogues on the iPad? Conceivably either solution will work, but a priority for a 1.0 product?
The catalog name is not important. I cannot see the catalog name in lightroom mobile, and I don't care which catalog the collection originated from. Behind the scenes, I imagine the collection would be named something like "catalogue A collection XYZ". The problem would only come up with multiple shared collections with the same name.
If the same file was shared in multiple collections, I could see that as being an issue. One that is solved by lightroom already. It doesn't matter if an image is in 5 different collections in lightroom right now, lightroom only sees the one image. If you edit the image in collection #3, then the same edits are reflected in collection #5. I'd imagine that some time delay may be present, but the same idea would carry over to the cloud. There is still only 1 image even if it is present in a dozen collections.
Don't underestimate the complications