Right now access to Marketplace/Compendium content is entirely account based and each GM only has access to content they've purchased themselves. Sharing Marketplace/Compendium content currently requires the original creator to manually import the content by dragging the compendium entries into the campaign ahead of time (thus bloating the handout/creature folders), dragging assets to spritesheet-like map pages so that they can be copied and manipulated by co-GMs (tiresome), or by downloading purchased assets and exchanging the zip archives (inconvenient, shady as shit, and also probably a ToS and/or copyright violation). Tying Creator's Marketplace/Compendium purchases to their campaigns and allowing co-GMs can also utilize them without needing to also purchase them would provide a convenient and legitimate way to share assets in a controlled manner. To avoid exploitation, say a community gifting all their assets to a single account and using it to create hundreds of simultaneous games run entirely by Co-GMs accounts, a limit could be set on the number of campaigns for which each account was allowed to enable this sharing. The number could also scaling with the account's subscription level (For example: 0 campaigns for Free accounts, 1 campaign for Plus accounts, 3 campaigns for Pro accounts). Sharing purchased content isn't an unprecedented concept for Roll20 as Co-GM's can already access module content imported by the Creator without needing to purchase it, though I realize in terms of implementation it is essentially the automated equivalent of the creator manually importing the content and that allowing Co-GMs to access a campaign Creator's Marketplace/Compendium content as though they owned it would likely be a non-trivial change.
