The development time thats gone into Blue - almost a year and a half - means that its a pretty substantial product, and we're trying to make it support all the things people have dreamed of since they first heard of MTA (and were inevitably dissapointed by its current release). Concequently, we believe that Blue is probably flexible enough for us to build on it for many years to come, unlike the current core which has grown too big for its (metaphorical) boots. That clearly means that we plan to release multiple releases based on blue. I supose change-wise, blue will be final for MTA, we won't start on a new core, the ammount of time invested in blue wouldn't make that practical, so whatever is release with blue will exist in all future versions (at least in principle).
eAi