Bring the gaming side in. Create online tournaments, painting competitions and army builds that either require or reward people to have a fleshed out Liber-stamped/worked through article along with their list/models.
It's funny you should say that - In my head I've been kicking an idea around for a thread that can be roughly summed up as "Liber Astartes kill-teams running around and hunting monsters, via the medium of play-by-post moves on a virtual battlefield".
Broadly, the idea was taken from a game held long ago (almost a decade back, I think) in the Space Wolves forum, where packs of marines went out hunting Fenrisian Kraken, and there was much telling of sagas and stories before and after moves. Granted, it's the Space Wolves, so a lot of it was about how drunk they were, but the idea could easily be leveraged for a Liber task force, replacing "staggering from the inhuman amount of ale consumed" to "behaving appropriately for their Chapter and/or adjusting their behaviour to better suit the Legio's requirements".
Adding a requirement for people to have posted and/or recently updated information for the Chapter they're representing wouldn't be too hard.
Of course I'd have to work out all the rules, and the terrain, and all the other minutiae of setting up such an endeavour, which will probably take me a whole year or two, but the idea's been there for a little while.
I took part in something similar on another forum years ago. We each had roughly 100p (or thereabouts) of units from the IG each with a designated character (such as a sergeant, or in my case an enginseer) as our individual PoV and would narrate our units actions through a campaign.
Battles where fought on a grid with marked terrain and so on and the GM would make all the dice rolls that you had declared and move markers for the units on the map. He even had small cardboard constructions for terrain and vehicles.
There would also be time at the staging posts where it was more casual just in character chat/actions/engagement with other participants.
I would be interested in such a play by post campaign again.