Both engines have different target users, and so we evaluate the priorities separately. Not only that, but having something developed for one engine helps in different amounts when it comes to developing the same feature for another engine - in some cases, some code can be shared, in some cases (most, really) only general pointers can be shared and most of the work still needs to be entirely redone as if from scratch, because the engines have very different codebases. Hope this helps explain the question on "sharing forces" :)
