Are there plans for more second editions, or are we done?
Since you skipped the small expansions - and card counts go up to 500 - Guilds, cornucopia and Alchemy don't have enough material to work in as a single big box second edition?
Second editions can't come out until the first edition of that set has sold through. And announcing a Second Edition could (theoretically) prevent that first edition from actually selling through. So this is a question that cannot satisfactorily be answered.
And Dominion second editions aside, it's generally up to the publisher to make announcements about upcoming products.
EDIT: Also Guilds and Cornucopia have already been combined into a large set, sometimes labeled "Mixed Box". Putting all three small expansions together would mean raising the price above a normal large box expansion I think, since it would be 450-ish cards, plus Coffers mats and coin tokens.