With texture compression, the textures wouldn't suffer too badly. The part that won't be up to par due to lower amount of RAM would be lower res shadows and not as impressive lighting if you are only talking about RAM, and not raw power alone, which Wii U would obviously not be on par with the PS4 either.
Title is weird BTW, it's more like "How will PS4 games fit on the Wii U" lol...