Exactly my thinking! I'm on the one plan at the moment (the unlimited data and tethering one) and pay £35 a month, which compared to the sim only at £15 a month for a 12 month sign up means your'e paying £480 over the 2 year £35 contract for the phone. I'd been looking to get a 64gb 5S which at £709 sim free would mean that if it cost £229 for the handset upfront and then still £35 a month, it would work out the same as getting it through Apple and having a sim only plan.
However now the cost looks likely to be £46 a month thats £31 more than the current sim only deal and so £744 extra for the phone over the 2 year contract. So even if they offer the 64gb for free thats £35 more over the life of the contract. But I'm guessing they'll stick on a, what, £200 ish upfront cost with it?
hmmmm decisions!