I just applied for the BGR with the 50k offer. If my goal is to keep one MR account open and maximize miles, why would I upgrade the BGR to a Plat rather than close the BGR and open up a Personal or MB Plat? The MB Plat has a 50k offer right now and would start the clock on the 12 month cycle. Unless you plan on keeping a Plat card open at all times (for the benefits), it seems to me the best churn/alternating approach is to keep the BGR until you want to sign up for a Plat offer (whether it's the MB 50k or hold out for a better one in the future), since the 50k MR beats the 25k upgrade offer.
It just looks to me like a 25k sign-up bonus for the $450 annual fee, albeit with no credit pull. Am I missing something?