Hightouch, an ad tech startup recently valued at $2.75 billion, has offered to buy LiveRamp's identity business from ad holding group Publicis for $800 million–$1.2 billion in cash and stock, according to a letter sent to Publicis' board last week and obtained by Axios. Why it matters: A fast-growing ad tech startup is trying to convince Publicis to sell off a significant part of LiveRamp before the ink is even dry on its acquisition.Publicis last month announced a $2.2 billion all-cash deal to...