The question is bit speculative but I think it can be answered. We don't know precisely what would happen but the worst case scenario is that you would be forced to leave your new job and return to Italy in a couple of years. The risk is there but, no matter the outcome, it seems quite small and it's extremely unlikely that anything would happen overnight.
If the UK leaves the EU, things like retirement pension or the status of non-EU family members when you return to your country of origin could also become more complicated. So if you are concerned about leaving your current job and not being able to find something you like in some years and absolutely cannot tolerate that uncertainty, waiting for the outcome of the referendum makes sense. But then again, switching jobs and especially countries always carries a risk that things don't go exactly as planned so if you are that risk-averse, maybe expatriation is not for you.
On other hand, it's conceivable that even if the UK leaves the EU, it will first introduce some kind of transition regime to “grandfather” EU workers who are already present in the country into the country's new visa/residence system. No matter the outcome, it's also extremely unlikely that immigrating would become any easier so from that perspective there is no reason to wait. And as @phoog commented, it's entirely possible that people who gained permanent residence or stayed for a yet-to-be-defined period of time before the transition would benefit from a special status so “starting the clock” as soon as possible might actually be advantageous.