Right now it's easier to invite players via an external URL than in the game world. Can we extend this to lobby-looking-for-group situations?

You might want to invite a handful of people to your personal instance of a world. (Not a world you wrote!) If you can generate a URL that does that job, it would be handy.

Where to mark this permission? It's not a question of giving the portlist an "external" flag; we need a finer grain. It's not even a link per se; it's a link+scope. And it has to be revocable.