There are at least two different commercial hosting sites that implement a pull request model. If you want ephemeral branches like in git, hg branches are indeed not the right choice. But that doesn't mean that they don't have their place. Try topic or bookmarks if you want gitish behavior.I have absolutely no clue what you mean with trunk-based development...
Funny, I rarely use branches (or topics) in Mercurial unless it is a complicated long-term project. Modern "everything on a branch" was invented by git users because the UI forces naming things. Mercurial allows sharing code and still linearizing history with rebase safely, so much less need for merges. I've always found pull requests to be only useful for the passing-by contribution. They are a pretty awful interface for anything else driven by GitHub internals more than anything else...
