As a GH user, I would like to be able set a capacity in hours per assignee (developer role) per version (sprint).

This is what I thought you might be doing when you implemented capacity planning in 3.7. Although I really like the new feature, the most common requested feature here is capacity in hours per person per version. I would also like this compared to the total original estimate for all issues in a version for that assignee and highlight it red if it is larger. We were thinking of a Resource Board where this data could be entered into a grid column. One row for each resource. Other columns could sum the original estimate and remaining on all their assigned tasks.