While I haven't fully read it, I know that someone at Team Covenant put together a rule system to introduce campaign mode to the Shadows of Mirkwood. Has anyone else done the same thing for the other cycles?

Would FFG ever consider doing something official?

You don't need to make the campaigns go from cycle to cycle. Just make a campaign within each cycle.

To me, this would make the game even better. They could create a pack to purchase like they do with the Nightmare modes.

The same person with Team Covenant also developed campaign rules for the Dwarrowdelf Cycle: http://talesfromthecards.wordpress.com/2014/07/22/dwarrowdelf-campaign/.

I agree that it would be great if FFG retroactively made some official campaign cards for the earlier/non-saga cycles.

Yeah it could definitely bring life back into older quests even more than or alternatively to what Nightmare does and a single POD pack per cycle with Campaign rules could be easy enough to make although I think they would have to add some type of boons/burdens, treasure cards or something else creative to make it worthwhile and have a unique campaign feel.

This was a great (if fan-made) attempt at creating new cards to support a Shadows of Mirkwood campaign (same one as alluded to in the OP): http://teamcovenant.com/davflamerock/2014/09/15/lord-of-the-rings-shadows-of-mirkwood-campaign/.

I ordered the set, but haven't tried it yet.