This is not what I asked. Recent SDK's (and SD's) doesn't support 51 and I wonder if it's due to some Nordic's policy to phase out 51 or not necessarily. We are using 51 in our product but will consider migrating to 52 for future releases of new features.
I asked my local sales manager the same question, just hope to get a faster response in here...
Intention of my answer was: you can either wait for Monday when Nordic support team will (with 99% probability) tell you the same as they say on all such requests on this forum (= any question regarding product availability and roadmap isn't part of the support but trade secret/business strategy and this can be discussed only with authorized sales person not on open forum) or you got it from me on Sunday. Sure, maybe you will get into that lucky 1%...
For details about software for nRF51 series, please see this answer. There is no plans to phase out production of nRF51 devices anytime soon, but I would recommend using nRF52 series for your future designs. The nRF52 series is a faster and more flexible chip, where you get the latest software updates.
