There is no knowledge about that… there is only the assumption that it is logical because the Shield is basically designed for Streaming services.
However, we also expect that it does not matter if the Exoplayer can do dual-layer DV. In case of the Shield can only do single-layer it is highly likely that it is limited to its own services (eg the built-in media player). That certainly does not affect external software like Plex (what comes along with the Exoplayer).
Currently it (the Shield) can’t play dual-layer because Plex uses an older version.
Playing dual-layer simply means that the respective player takes the enhancement layer into account when playing the media. Currently Plex ignores it as it does not know what to do with it. Accordingly, I would expect that the assumption that the Shield can only do single-layer is limited to its own services.
Even if not… I would further expect that it is rather a licensing related limitation than a hardware based limitation.
