I implemented a similar BiLSTM-CRF model at my current job. The architecture itself is really interesting, but runs into scaling issues. With LSTMs, you run into the constraint of having to wait on previous inputs and cache those results as well. Although TensorFlow now offers Cuda RNNS and fused kernels to speed up computation, I'd have thought for Amazon's scale, an attention/transformer based architcture would serve them better.

I also notice a lot of dismissive comments about "black box models" or the simple solutions of just parsing out whitespace. My two cents:

1. Models with hand crafted rules perform WORSE than learned representations, especially when you have an end-to-end model with pre trained embeddings. This is shown by one of the seminal papers on this model, Ma and Hovy (2016) https://arxiv.org/pdf/1603.01354.pdf.

"However, even systems that have utilized dis-tributed representations as inputs have used theseto augment, rather than replace, hand-crafted fea-tures (e.g. word spelling and capitalization pat-terns). Their performance drops rapidly when themodels solely depend on neural embeddings"

2. Human speech and human written text are messy. Having a rule for human speech will inevitably lead to a massive list of rules and exceptions to those rules.

3. This model is multi domain, meaning that you don't just need rules for one domain, but rules for multiple domains and interactions between those domains. Considering Amazon's hefty amount of data, it's much more efficient to learn these represntations though a machine learning model rather than constantly playing cat-and-mouse with keeping your hand crafted rules.