The new releases of Outlook for IOS, Android and Windows Phone all have this feature.
I'm afraid the answer is no. You can install the Office 2016 preview version to verify it.
I continue to be baffled as to why MS will not add a unified Inbox capability to Outlook (for Windows). The recent releases of Outlook for both IOS and Android have this capability, as do several of the 3rd-party mail clients for Windows (e.g. emClient). I use emClient primarily for this feature (I have 2 outlook.com email accounts and 3 Gmail accounts), but it (emClient) lacks the many formatting, view and integration features that Outlook has as part of the Office suite.
The unified Inbox workarounds for Outlook, of which I've tried several, all have holes in them (i.e. not all messages make it to the unified Inbox reliably) and are very fragile.
I'd be willing to shut up about this (for a while) if only someone could explain MS's reason for not adding this to Outlook 2016. I just don't g