It is probably opt-in and a crippled version of the default chat interface. This way the few users of the feature will be visible like a Christmas tree in a da

It is probably opt-in and a crippled version of the default chat interface. This way the few users of the feature will be visible like a Christmas tree in a dark forest and the general userbase will think it's their laziness not to use encrypted Skype. That's also how Facebook implemented it in messenger.