42 minutes ago, Khudzlin said:

I seriously doubt it. Weaknesses (like story assets) have a player back (for the same reason: they're meant to be shuffled in a player's deck, not in the encounter deck). Cards with different backs don't get shuffled together (remember that player-backed cards owned by the scenario are removed from the game instead of going to the encounter discard).

Again, that's our current understanding. There's nothing about Weaknesses that require them to be player-backed cards. It could be something that once drawn off the encounter deck, enters your threat area and remains there until the end of the scenario; or even has the Permanent keyword and remains there until the end of the campaign.

28 minutes ago, Network57 said:

Again, that's our current understanding. There's nothing about Weaknesses that require them to be player-backed cards. It could be something that once drawn off the encounter deck, enters your threat area and remains there until the end of the scenario; or even has the Permanent keyword and remains there until the end of the campaign.

except that

Quote

If a weakness is added to a player’s deck, hand, or threat area during the play of a scenario, that weakness remains a part of that investigator's deck for the rest of the campaign. (Unless it is removed from the campaign by a card ability or scenario resolution.)

20 minutes ago, Network57 said:

It could be something that once drawn off the encounter deck, enters your threat area and remains there until the end of the scenario; or even has the Permanent keyword and remains there until the end of the campaign.

There are already treacheries that enter your threat area when drawn (like Frozen in Fear), and stay until you get rid of them or the scenario ends for you (all enemies work that way, too). As for your other suggestion, Permanent means "starts in play" as well as "can't leave play", so it doesn't work. We're more likely to see card effects, resolutions or setup instructions that make you add weaknesses to your deck (and it's already been done).