Hey @broke.eth, welcome to the forums! Really cool first post…
Using a “showcase” key could work as @liubenben mentioned, but then platforms would need to adhere to that standard in order for it to filter out items in a standard way. Plus, adding and updating that amount of data to a record on L1 would be quite costly in gas.
What might also be a solution is for a marketplace (or some third party) to create a filtering service, and then a service key related to that. You can read more on service keys ENSIP-5.
I guess similar to how OpenSea’s Seaport Contract can be used across marketplaces, some type of filtering service could be used by multiple platforms/dapps/wallets.
DM3 makes for an interesting use of service keys. Different idea (they are a messaging protocol), but use service keys in ENS records in a unique way.
Something like: com.nftpreferences.showcase as a service key, but the service nftpreferences[.]com would need to actually exist, maintain the preferences (JSON file or something), but then also platforms/wallets/dapps would need to rely on that service key (and the service) to know what are the items that should appear in a user’s “showcase” of NFTs.