No clue if they'll read this. I hope they do, 'cause this one struck me out of the blue, and it seems so *straightforward* I'm amazed I never thought of it before!
Okay. First, we know the Foundry concept from STO doesn't work with Champions because it's an older platform, and bolting it on doesn't work. This is what's prevented people from coming up with player-generated content.
Second, the Devs have recently been holding costume contests, with the winning entry being built as a new in-game update, adding new costumes to the game. It works well, and the playerbase gets really involved in the outcome.
See where I'm going here? The Devs hold a contest for people to come up with a new mission. Make it a muliti-mission arc so as to increase replayability for everyone. Maybe a 3 or 5 mission arc. Obvious rules things like it having to fit the storyline, it can't be an obvious ripoff of someone else's property, and for interest's sake, it should be as original as possible. That kind of thing.
Then hold a contest for two or three weeks, for people to submit story ideas. This includes proposed combats, locations and even dialogue. The winner, picked by the Devs, has their work turned into story-arc which is added to the game, through an NPC who hands these things out. Then just turn out one arc every month, with a development delay time of two or three months from winning to deployment.
At first, the number of missions will obviously be small. But in six months? A year? Eventually there will be a large list of player-generated content added by the devs which will greatly increase playability of the game content. It neatly steps around the Foundry issue by allowing the Devs to script the new missions and add them, but also allows the players to contribute, giving the Devs the ability to tap all that creative power the playerbase has at its disposal.