Complex card data using properties

Inspired by how BDs are constructed in Notion or Appflowy, I would love for decks and cards to be able to get "tagged" with specific data types using "properties".
Instead of tags that permit sorting only within a single deck, properties could perhaps be used to connect cards together, connect cards across different boards, and could also be used to call cards to be displayed by filters , perhaps addressing needs expressed in #6494 and other similar asks.
Especially, I would use an ability to relate one card to another as a means of this to jerry-rigging dependencies.
For exemple, if I could have a deck i'd call projects, and I could create a "relation" property to another deck I call tasks, I could identify tasks related to a project while maintaining the "task" card's full independence.

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No source files, tests, or entry points are identified; begin by reviewing the existing tag and card model and related issue #6494. Define the property and cross-deck relation behavior before implementation, with completion requiring cards to support related data and filtering as described.