So, I am just re-reading the Horus Heresy books (well I might miss out the abyss and the DA ones but anyway).
And it got me thinking - I know the HH has been done by BoLS but wouldn't it make a great GW worldwide campaign, like Armageddon and Medusa? Apoc sheets, maybe a codex (yes I know I know don't delay army x its been x years).
Another possibility would be the whole End of Times - the Golden Throne on the way out, aliens on the door step. Take 40k to its next epoch - fight the battle and if the Imps win then we get a new period of crusade, if the xenos/chaos/non-imps win the imps are forced back into some sort of new age of strife (until a future campaign when we fight to get back on track.)
My tuppence is Horus heresy, what do you think?