Is it really only integer scaling? Bit of a bummer if so. I'd have hoped they'd design arbitrary scales into this or it'll be stuck behind Windows and OS X for potentially a long time (until someone fixes it and all of the 3rd party software is updated to work right at other scales).
I run my Windows computer at 1.5 scale, which gives me sharp but readable text and a whole ton of screen real estate.
Who wants to buy an expensive 28" 4K screen and either choose between huge interface with 1080p effective resolution or an unusably tiny interface at native 4K?
Is "arbitrary widgets" everything that isn't text, including the overall layout of a window? That sounds a lot like Windows' "Change only the text size" option, which has been around for a long time and isn't a good substitute for UI scale.
Size of all of the mouse targets is as big a deal as the text; they need a middle ground between "impossible to hit" and "gigantic waste of space".
I'd just been getting in to Linux (via the LF course on edX) and have it dual booting on my old laptop, but all of my newer computers have higher res screens that fit best at fractional upscaling from the "standard" size of old UIs. Guess I'll keep working on it because I'm enjoying the CLI and playing around with a web server, but I'm now a lot less excited about the prospects of Linux as a Windows / OS X replacement.
The GNOME 3 stack does better than Windows at scaling UI elements based on text size; I'm successfully using a 1.4 or 1.5x scale on a 2560x1440 14" screen, and none of the UI elements look too small to me. Off the top of my head, I think the main elements that DPI-based font-size scaling doesn't scale are raster images (for which HiDPI allows supplying alternate high-res images similar to CSS) and cairo-based drawing elements (see cairo's "device-scale" support).
This is from March.