Workboards require the full screen to work as intended, they are not compatible with Dashboards in it's current state. There is a longer term plan to provide some sort of "Dashboard Workspace" which lets you embed multiple dashboards into your homepage, but thats more of a v2 feature not likely to be gotten to for some time.

Oh :(

Can't we put this into a <div style="overflow:scroll"></div> or something?

Yeah, there's just a ton of work between where this is and getting dashboards embedded as a panel. We might pursue it, but this approach (roughly: duplicate all of the rendering code) isn't the approach we would want to take. The plans for dashboards/workboards aren't completely clear yet, but we'll probably launch dashboards and get workboards much farther along before we try to figure it out.

If you find this useful, you can drop it into phabricator/src/extensions/ and use it on your install without upstreaming it. (You may need to keep it updated as we change things in the upstream, of course.)

What problem specifically are you trying to solve? Would embeddable 'Fact' Widgets about Projects be equally interesting? It's designed out to be more of "launch status overview" in a small space. https://secure.phabricator.com/uiexample/view/PHUIInfoPanelExample/