> kNN combined with embeddings from pre-trained deep learning models can be very useful for information retrieval
Indeed! We've been able to build simple reverse image search apps and other solutions using the power of embeddings from pre-trained ML models: https://gist.github.com/fzliu/c9380a7f9ba411adeff0b727cdba15....
One quick note: k-d trees are great for indexing low-dimensional data, but for high-dimensional embeddings they tend to be a poor indexing choice since you'll end up visiting more nodes in the tree than you'd like. I found [1] to be a great overview of different indexing types for high-dimensional vectors and the advantages of each.