This bug was closed before as WontFix

https://bugs.chromium.org/p/chromium/issues/detail?id=707797

Does this mean it's actually going to be fixed? 

Also, using a command-line option of 

--force-device-scale-factor=1.5

works, but it will apply to all monitors, so it's only a partial workaround (and it requires Developer Mode)

Yes. The bug will be fixed. The patches are already in progress.

"--force-device-scale-factor=1.5" is a test feature and is not a full proof solution and leads to numerous bugs if used in production.

Were changes already made to support this?  When I connect a 4K display via HDMI 2.0 through USB-C, Chrome OS recognizes the display, defaults to its native 3840 x 2160 resolution, and applies a scale factor which looks approximately like 2x scaling.

That is probably better than native resolution for most people, though unfortunately it is not for me - I use a 55" 4K display (well, TV... LG EG9600), and I do sit just a couple of feet away on a regular computer desk, so I don't need/want scaling.

If the current implementation is just a default and the user will ultimately have the choice of scale factor, that'd be great!

Follow up to #5, that was on Chrome OS 61, using a device on the beta channel (I'm not on that machine now so I don't have the exact build handy).

Any idea what release might have these fixes or if we can test it now?

Also has anyone else noticed that Android apps like Inbox get really pixelated fonts when you adjust the resolution to anything else other than 1080p scaled on an external 4K display? It would be nice if Android was in better sync with Chrome OS about it's UI.

For example I'd rather have a smaller display size on my external 4K display. But on my Chromebook, I don't want that. Also if I adjust the Android screen size, that messes with the mouse pointer.