It's almost over for lumia and blackberry. So why not unite and deliver a combined ecosystem. Bb10 +Iive tiles+ office 365 + here maps + best of lumia HW and bb HW + amazon store.
BB is already cozy with Android and it seems to be helping sales. The only thing that appeals to me is BB10OS, and that isn't in the realm of possible with W10M. Just keep bringing over BB10 features to W10M.