Jonny and Kate's final week tactic has revealed itself. Having heard from outside chants that Tim's unpopularity is apparently because he is "boring", they see this as the key to winning.
Labelling is a powerful device with which to colour the public's perceptions - Hence suddenly Jonny & Kate's repeated references to themselves being "in here to have fun" and Alex & Tim as boring / humourless/ needs to lighten up, both in conversation and as nomination reasons.
Interesting also that Jonny was saying to the others how silly of Alex for thinking of walking, so close to the end. Didn't Jonny himself say to BB in the diary room only 2 days ago that he "woke up wanting to walk"? Judging by his criticism of Alex today for contemplating the same, we can only deduce that Jonny's latest claim of "wanting to walk" was totally insincere and an act. If he had been sincere about that, the natural human response would have been to empathise with Alex's feelings of wanting to go by saying "yes, I felt the same way only a couple of days ago". Instead Jonny's response was the opposite.
This is only one of many examples of Jonny's behaviour not consistent with what he says. Nothing wrong with having a gameplan of course, but he is masquerading as Mr genuine-nice-guy-who-has-no-issues-with-anyone, when analysis of the evidence strongly suggests otherwise. Just as it's fair play for Tim's cover-up of his true hair colour to be revealed, so Jonny's fake persona deserves to be exposed.
I suspect many will be unconvinced by Jonny's apparent reluctance to nominate; people can often tell if someone's being contrived without being able to pinpoint exactly why (sometimes referred to as a 'sixth sense'). Also the issue of 'Jonny: genuine or fake?' has intruded into public consciousness, so people are more likely to look to pick it up.
I also think Jonny & Kate's attempt to label Alex as joyless and boring will not stick with the public, particularly as the final is in sight. Most viewers, I suspect, will decide their vote based on the entire programme run. Jonny-supporters may assert that Alex is boring and unfunny, but general consensus would seem to contend otherwise. eg. Phil Edgar-Jones, BB exec. producer (newspaper interview): "I think Alex is fascinating...so many layers to him"; Dermot O'Leary (BB magazine): "[Alex} is far and away the most entertaining guy in the house by a country mile."