A Supermarket News story recently quoted an analyst who predicted that the "invasion" of Lidl into the U.S., combined with Aldi's rapid expansion, will prove to be problematic for smaller operators and those focused on lower-income shoppers. The analyst did not think the two European powerhouses would have as devastating an effect on top U.S. grocers.
However, based on where Lidl is buying property in the Greater Philadelphia region, it certainly appears they believe they will have a big effect on top grocers. From what I have seen, they are eager to open up stores adjacent to - or across the street from - market leaders Giant and ShopRite.
Although they are opening new stores all over the country, Aldi's recent growth has been mostly focused on California. Lidl is planning to open at least 75 stores from New Jersey to Georgia in early 2018.