I've always used browser execute javascript for switchGameAsync: "FBInstant.switchGameAsync('"GAMEID"');"
Since it was a simple function with a simple workaround I don't mind for it to not be supported by the plugin.
But there is some key features pending to be added yet, like chooseAsync, and I (and I think anyone) don't want to rely on a third-party plugin for it. So we got enough features for what we need or enough for scirra to promote C3 as supporting Instant Games?
Also posting in the suggestion platform seems pointless. That place looks abandoned.
Sorry for being salty here, I know scirra is very busy with C3 runtime (wich seems great), but I think the pratical solutions now is more urgent. Platforms like Instant Games is one that enables developers to monetize their works also enabling developers to keep their C3 subscription.