I’d like to see the inbox as part of a “plan” perspective that includes all my projects distributed in various folders. That used to be possible in OF1.
In previous forum threads, it has been discussed as not possible. But it seems like a popular feature request. Send a feature request e-mail to email@example.com to put your vote in.
For now, having two windows side by side is the current compromise. Then you drag and drop between the two windows.
For reference: this is the thread wilsonng is talking about: Viewing the Inbox at the same time as Projects? [Available in v2.10]