Thanks for the links, Luke! It looks like Pepper already has an ELAN import module, but maybe it doesn’t have a JSON export module.
So it sounds like they are essentially trying to do what @pathall had in mind, but use the Salt model in the middle instead of JSON:
The aim of Salt is to consolidate all kinds of annotations within a single model. For doing so we need a powerful base structure, which can cover all the different necessities at once. A very well-known and powerful structure in mathematics and informatics is the common graph, which is widely used for modeling very different kinds of data. The graph structure has a further benefit in that it helps to keep the model simple with its small set of different model elements. Our graph structure is rather simple, it only contains four model elements: node, relation, label and layer.
Could we say then that Salt has the advantage of comprehensive support for all potentially relevant features, but JSON has the advantage of ease-of-use/interoperability?