Windows Continuum is a wonderful concept, so good Samsung pinched it for its flagship Galaxy S8. The limitation of both approaches is the availability of the input and output devices which make the solution so valuable.
Great for going from office to office, not so much for those impromptu coffee shop or mid-flight updates.
Could a phone be made to work in these circumstance? Only if the screen were large enough and a suitable input mechanism could be devised.
Turns out Samsung already has the answer to this question in the Galaxy Note range. Its pen input adequately replaces a keyboard and mouse for most uses, providing hover, mouseover and precision selections; and providing an input panel which can be small enough to enter reasonable amounts of text without obscuring a large part of the screen.
If Samsung ships the Note 8 with the screen of the S8+ (or even slightly larger) and includes support for the DeX dock, it will have a product which really could be your one device to rule them all.