Sequence to Sequence (Seq2Seq) models

When learning about time-series models, we might have come across various sequence learning problems such as Stock Market Prediction, Story Telling, and AutoComplete that could be learnt by traditional neural networks like the Recurrent Neural Network (RNN), and Long Short-Term Memory (LSTM). But, will these Artificial Neural Networks (ANNs) work even when the problem gets complicated? Seq2Seq models are a special class of models that make minimal sequence structure assumptions and could be used to solve complex sequence problems. Let's discuss the Seq2Seq models on the following topics. Which of these tasks do you think could be solved by a single neural network?