Yeah, I think it would be good to be able to either define font sizes in px or in vw. When defined as vw, the font size resizes with the browser. https://css-tricks.com/viewport-sized-typography/
Should only be used for big text though. Small text could become way too small at a certain size. Like here: http://shop.mango.com/iframe.faces?state=he_004_AL
:scream:
Edit: In version 1.022 the font-size can now be set in % in Text Formats and the Customizer