Well it appears one of the developers for Rainbow Six: Siege, Scott Mitchell, has let the cat out of the bag about something called Rainbow Credits that will appear in the game. These are different from the current earn-able in game currency called Renown which can be used for unlocks, but aside from the small slip there are no details about the credits. The revelation came from an interview conducted by Angry Joe, with the moment occurring at approximately the nine minute mark in the video below.
Joe asks Scott what Rainbow Credits are at which point Scott turns to a member of the PR team. He asks whether they’re talking about the credits yet and is met with a firm no. Ubisoft may not be talking about them yet but others are, so we’d expect some news on them soon. Whether they are microtransactions or a different type of in game currency is yet unknown.