Arial was first created in 1982, and has served the web well for decades. But technology moves on. Modern system typefaces look better on both new high DPI screens, and old screens alike. Apple’s San Francisco and Microsoft’s Segoe both look great on retina displays, have more expressive weights, and improve readability across all contexts.
To me, Segoe UI looks like a cartoon comic font. It's really bad, and unreadable. And I am not alone in thinking this.
Also, IMO Arial was perfectly readable on my HP 24mh monitor, with my Nvidia GeforceGeForce GTX 1050 tiTi video card (this is new tech on the market). Yet the font is unreadable on this new technology. And I don't see any data that proves system typefaces look better than arialArial on new devices.
Is there any paper which uses data collected from people that states that system fonts are more readable than Arial? Really, one of the only reasons this change was made was because GitHub did it.... :\
If you want to switch the font, please make it something other than Segoe UI for windowsWindows.
Finally, italics are a pain to read in the new font.