I'd honestly be surprised if there is a switch to ITV branding any time soon. If it were to happen, I'd expect dual branding first, with small ITV logos appearing at the bottom of the idents and "ITV News" appearing on the UTV Live titles.
UTV viewers are already exposed to a considerable amount of ITV branding - be it ITV Studios stings, trails for ITV 2/3/4/Be/Encore, ITV Box Office promos or new season programme trails for ITV which are popping up in between ads. And of course, the full portfolio of ITV-branded channels is available to NI viewers anyway - and they quite often run ITV-branded trails for the main ITV channel (conflicting with the UTV-branded versions of the same trails on UTV).
I can't see this being the long drawn out affair that we experienced with the phasing out of the ITV English/Welsh regional brands. ITV has completely refreshed UTV's on air look - pretty soon after taking control of the company. I believe the relatively quick pace of change will continue. I do believe they were right not to dump the UTV brand last October. They will have wanted to tread carefully, for various reasons. One of these being to preserve the high ratings share UTV has here. It's a relatively small population, yes. But money is money. But even with a completely new look, ratings are as strong as ever.
Complete speculation but I can't see them going for a big bang switch to ITV branding. I do think it'll be phased in and I do see daytime as a prime candidate for a first strike - potentially switching to full ITV branding (trails and idents), with prime-time retaining UTV idents for a while longer. Not sure I see a situation though where UTV and ITV logos will appear together on trails or idents.
Other than people like us, I doubt that many people will actually notice or give a toss when that UTV logo becomes an ITV logo - it'll be such an insignificant change to most people.