The Uno WiFi Rev. 2 uses a different, and fairly new processor with very different peripherals than those on the '328p. It is a more capable chip, but there are far fewer libraries that support it compared to the '328p - anything that directly manipulates registers is not compatible (the register emulation feature only works in some very simple cases, and in at least some of the cases where it "works", it obviates much of the benefit of using direct register access). So this could either be a great choice if you don't want to use any libraries that happen to not be compatible, or make things a lot harder if you do. (Compile errors complaining of undefined variables with names composed of capital letters and numbers are the symptom of this)