Yeah, you're not likely to get many big discounts from Lego themselves but sometimes Amazon/John Lewis/various supermarkets reduce the big sets by a decent amount. The big Technic Supercars usually appear in Black Friday sales with at least a hundred quid knocked off. The Disney store cut a hundred quid off the UCS Star Destroyer, too. So it's just a case of keeping an eye on various stores, unfortunately.
I think it will depend how well the sets actually sell, too. They've reduced the helmet collection a few times over the past few months, so obviously I wasn't the only one who thought £55 was far too much for them...
They mention the Horizon set is their "first" Sony tie-in, so there's presumably more coming, but they haven't really given many hints as to what any other sets could be. Wonder how much of a payout Mega Bloks are hoping for for the Halo license...
(I think they've still got the Pokemon license too, so they might be quids-in if Lego really do go all-in with video game licenses)