Like so many things with regards to engineering, this is a modern application of an old idea.
That's not a criticism, just how it is. Do some research into the incredible amount of fantastic ideas that have been tried, but abandoned because of materials technology, low tech available when the design is first tried, and you will be amazed at what has been already thought of.
I think, that this opposed piston engine is reminiscent of a Junkers aircraft engine. It's Very Clever design, that has been vastly improved on.
I also think, that Bill Gates has backed this, contributing a fair few million to it's further development. But I might have it mixed up with another project?