1. For me, the contiguity principle just looks like they are using big words for a very common-sense idea. If you present the same thing in three different forms but they are widely separated in time or space, students will get confused. Have I misunderstood?
2. For non-native speakers I agree with Allison that the modality principle is perhaps less of a benefit than with native speakers – you can’t depend to the same extent on their listening comprehension. However, I think it’s more about building enough time for processing into whatever you are presenting and if we are thinking of asynchronous learning, where the students can go at their own pace, the problem is diminished.