I hope so too. I bought the PHB2. But I be quite willing to buy another in a boxed set. Especially since it will be cheaper in total for all three (I am gonna use Compendium for now for MM2 and DMG2 will hopefully be followed shortly by the boxed set).
It's one thing to collect all three core books, and another to collect three expansions, which, whatever Wizards says, are not 'core' in the same sense as the core books.
I can more likely see Player's Handbook, Monster Manual and DMG giftsets once the threes are out, a PHB set is pretty useful for a brand new player, or one who's been playing a while and just borrowing the DM's books.
They did this in 3e - I believe for 3 of the environment series and maybe 3 of the race series but it was around xmas and sometime after the books came out. i am guessing because they had back stock.