Should the Blender SE site be targeted towards Blender users or developers or both?
I think that focusing on the end-users is the way to go. The Blender developers would probably be asking questions that don't apply to creating 3D art; they would probably be more interested in asking programming questions about how to create functionality in Blender which would fall under StackOverflow's domain. I think it will be imperative to get the Blender developers to act as the site's experts, answering questions rather than asking development questions.
IMHO, the site should cater to end users, but it should also allow for a scope that includes:
It should not cover:
Since the Proposal is still in Definition phase, that is honestly the sort of thing still to be determined (the range of topics and audience) primarily by the process of posting and upvoting/downvoting Example questions.
However if you have an interest in the proposed forum for one reason or another, and don't feel it would be well expressed by posting Example questions, then perhaps it would be good to articulate your interest with a "self-answer" here.