It's only in the last 12 months that it became clear this was possible. The Ng "Zero Shot Learning" paper came out at NIPS2013, and given the lead time for a paper like that I think they must have started work at about that time.
There are many machine learning libraries that have good implementations of LDA (e.g. Gensim), so it should be "relatively" straightforward to create the topics and clustering based on the abstracts of the papers.
But one of the listed papers is also by Kapathy ("Deep Fragment Embeddings for Bidirectional Image Sentence Mapping"), and I think this might be what nl is complimenting as being done quickly.