We're using Portfolio for JIRA not just to manage "people" resources, but (through virtual users) to schedule certain physical resources that are required for some projects.
This works nicely as long as the thing being scheduled is a Story or Bug.
Stage 1: 2 hours of Skill A (Resource A)
Stage 2: 2 hours of Skill B (Resource B)
Stage 3: 4 hours of both Skill A and B
For stories, this does exactly the right thing: both resources are kept busy and nothing is overbooked: for the third stage of work both resource A and B will be used. This fails if the same scheme is applied to Sub-tasks:
"No single user has the necessary skills..."
That seems like an artificial constraint, in that it doesn't apply to other issue types, only sub-tasks. There's mention in the Portfolio FAQ that the number of users that can be "assigned" a single issue in Portfolio is configurable, but I don't see that setting anywhere; nor is there a mention of that limit being configurable by issue type.
There are no plans to actually assign these users to anything in JIRA-- this is all virtual scheduling for planning purposes. Could that constraint be relaxed somehow?